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The Geology of the San Juan Islands



The limestone deposits occurring in the San Juan Island region are confined to Orcas Island, San Juan Island, Shaw Island, O'Neal Island, Henry Island, Jones Island, Cliff Island, and Crane Island. These deposits occur in rocks of Devonian, Carboniferous, and Triassic age. They are particularly abundant in the cherty formations of the Orcas group, and occasionally they are found interbedded with the sediments of the Leech River group.

The limestone deposits occurring throughout the whole region have a marked tendency to pinch out rapidly in every direction. They generally occur as small "pockets" in the Orcas cherts, and each deposit is typically lens-shaped.


When a rock is crushed or pulverized either by hand or by the natural processes of weathering, and the resulting material is sorted by the action of water, the following products are obtained:

(1) Coarse fragments which in nature are deposited close to shore in the form of gravel.

(2) Finer fragments which are carried farther from shore by the action of waves and currents and finally deposited as sand.

(3) Still finer fragments which are carried far from shore by the action of storm waves and tidal currents and deposited as silt or clay.

(4) Extremely fine particles which form a colloidal suspension in water. The nature of this material is such that it is carried long distances from land. It tends to settle out during quiet weather, but it is again transported in one direction or another by each succeeding storm, until it is finally covered by other sediments.

It is assumed that the cherts of the Orcas group were formed by a semi-colloidal silica silt which was distributed over the bottom of an epicontinental sea far away from the shore. The conditions of sedimentation were such that thin alternating layers of semi-colloidal silica silt and argillaceous silt were being deposited over a wide area.

The bottom of this sea was apparently unfavorable for plant or animal life. Isolated colonies of corals and other sedentary animals and plants occurred here and there but the struggle for existence was apparently very keen. In some cases the colonies of corals were able to thrive temporarily and they grew up higher and higher and spread out rapidly on all sides. Then the conditions changed in such a manner that the struggle for existence became more intense. The animals near the margins of the colonies were evidently less favored than the others and they were unable to survive. In the mean time the siliceous and argillaceous sediments were accumulating, and when the margins of the colonies failed to grow upward, they were covered with sediment. Thus a colony of lime-secreting animals or plants might gain a foothold on a small area; grow upward and spread outward as the deposition of sediment progressed; after reaching a period of maximum development, to gradually dwindle down to extinction and to be finally covered by later sediment—such is the apparent origin of the lens-shaped limestone beds which occur in the sediments of the Orcas group.

The limestone lenses or "pockets" which often end abruptly without any tapering, are in some cases truncated by faulting, and in others by the intrusion of igneous rocks. The more rounded masses of limestone were apparently produced by the intensity of the forces which folded the rocks of the Orcas group. The original limestone strata were considerably more extensive than the ledges occurring at the present time.


The largest deposit of limestone occurring within the map-area is located at Roche Harbor near the north end of San Juan Island. The limestone deposit is located on the elevated peninsula which separates Roche Harbor from Westcott Bay. The quarries and the lime-burning plant at Roche Harbor, which belong to the Roche Harbor Lime and Cement Company, are the largest lime producers in the State of Washington.

Under the management of John S. McMillin the lime-burning establishment has been built up until, at the present time, it is equipped with the most modern appliances. The lime-burning plant at Roche Harbor has been described in detail by Landes.40

40 Landes, Henry, The Non-Metalliferous Resources of Washington, Except Coal: Wash. Geol. Survey, vol. 1, part 3, pp. 24-27, 1902.

After being newly equipped with eight modern kilns of the bottle type, the plant suffered from a disastrous fire during the summer of 1923. Although this loss was keenly felt and the industry was practically paralyzed at the time, it did not prevent the company from pursuing a continued policy of expansion and enlargement.

Previous to the fire of 1923, many of the buildings were being utilized almost beyond the limit of their capacity. As in the case of most disasters to well established industries, the evil effect was temporary, for the destroyed portions of the equipment are already being replaced by newer and more efficient appliances which eventually will greatly increase the output.

The limestone, which is very compact and completely recrystallized, is broken loose by blasting. (See Plate XXI-B.) The loosened product is then broken by hand into lumps of the desired size, and at the same time it is sorted and classified according to its quality. The classified lumps of limestone are delivered to the nearby kilns by means of railway cars, and these are emptied into hoppers which lead by gravity into the kilns below. The kilns are situated along the shore of Roche Harbor, and large warehouses and shipping docks are located near at hand.

The limestone deposit at Roche Harbor is situated in a region which has suffered from intense folding and faulting. A fault of considerable horizontal and vertical displacement crosses San Juan Island from Rocky Bay to Roche Harbor. The northern end of the Roche Harbor limestone deposit is evidently truncated by this fault, and the northern side of the fault evidently moved westerly or northwesterly with respect to the southern side. If this is true, the northern extension of the limestone strata exposed at Roche Harbor should occur at the bottom of the Haro Strait somewhere to the west of Battleship Island.

To the south of the fault or fault zone, the Orcas cherts are folded into the form of a broad syncline plunging towards the southeastward, and the region in the vicinity of Mosquito Pass is located on the axis of this fold.

The limestone deposit at Roche Harbor is apparently composed of several limestone strata which are separated from each other by interbeds of chert and argillite belonging to the Orcas group. The large accumulation of limestone at this locality is not due to the thickness of individual strata. As a result of the intensity of the folding in this area, the folds have been locally overturned, and as a consequence each limestone layer is repeated at least three times in the quarries making up the Roche Harbor limestone deposit. Although three large quarries, and several small ones, have been developed, the limestone reserves are of considerable magnitude.

The Roche Harbor limestone deposit is relatively free from intrusions of igneous materials and these have in no way injured the quality of the stone. The fact that Bazalgette Point is composed of igneous rocks derived from the late Jurassic intrusions, would indicate that its close proximity to the limestone deposits has been brought about by faulting, for otherwise the limestones would surely have shown the effect of the intrusions. The only igneous material which actually cuts the limestone deposits is some greatly altered sill-like andesitic material. These igneous rocks are possibly a part of the Eagle Cliff porphyrites, and their intrusion apparently occurred prior to the period of major faulting.

The limestones, which are typically coarse to medium-grained and bluish-gray in color, are completely recrystallized. Their purity and uniformity of composition throughout the deposit is remarkable, and it is easily practical for the company to guarantee a content of calcium carbonate in their product exceeding 98 per cent. The percentage of magnesium carbonate in all of the limestones of the Orcas group is very low, usually being less than one per cent. This is all the more remarkable considering the fact that the whole region has been repeatedly intruded by rocks containing high percentages of magnesium.

The following analyses41 show clearly the remarkable purity of the Roche Harbor limestone:

41Landes, Henry, Cement Resources of Washington: U. S. Geol. Survey Bull. 285, p. 378, 1906.




I. Analyzed in 1888 by Moss Bay Hematite and Iron Company (Limited), Workington, England.

II. Analyzed in 1893 by Puget Sound Reduction Company, Everett, Wash.

III. Analyzed in 1902 by C. F. McKenna, New York City.

Small limestone deposits may be traced southward and southeastward from Roche Harbor intermittently for several miles. These lenses do not belong to a definite horizon. The fact that the cherts on Mount Dallas Range contain small lenses of limestone scattered throughout the whole area, would tend to make any correlation of the lenses in the Orcas cherts very doubtful.

In 1923 the Orcas Lime Company, which for several years operated a limestone quarry on Orcas Island, opened up a quarry about half a mile south of that operated by the Roche Harbor Lime and Cement Company. The quarry is located on the peninsula between Westcott Bay and Mosquito Pass. A lime-kiln of the bottle type has been installed and a wharf has been constructed on the shore of Mosquito Pass. The limestone is conveyed from the quarry to the kiln by gasoline-propelled cars. As yet but little development work has been done in the quarry and the size and quality of the deposit has not been proved.

Small scattered lenses or fragments of lenses of limestone occur at Mitchell Bay and along the shore to the southward.

On the west shore of San Juan Island near the foot of Mount Dallas Range, in section 23, T 35 N, R 4 W, there is a large limestone quarry belonging to Henry Cowell & Company. The deposit was known to the earliest settlers and has been quarried for a number of years. The early settlers regarded this deposit as a much larger one than that occurring at Roche Harbor.

Unlike the Roche Harbor deposits it has been silicified to a considerable extent by intrusions of the Eagle Cliff porphyrites. The igneous dikes have added little except silica in the form of flint, to the limestones. The flinty limestones so produced, when mixed with the enclosing country rock and burned, makes a good quality of Portland cement. The unsilicified portions are burned in kilns constructed of Sucia Island sandstone and lined with fire bricks. The quarry is located about two hundred feet above the kilns, and the rock is delivered by means of cable cars using the gravity system.

The remaining limestone deposits are not being worked at the present time. The majority of them are too small to be worth quarrying, while others have been quarried to the point where they are no longer profitable.

A large number of small limestone lenses occur on Mount Dallas Range. In many cases the individual lenses do not exceed fifteen feet in length and two feet in thickness. An examination of the enclosing chert strata often shows that no faulting has taken place to truncate the limestone layers. Occasionally it is possible to follow the courses of the chert strata from one lens to another and demonstrate that no faulting has taken place between them, and also demonstrate that the lenses do not belong to the same horizon.

Two deserted limestone quarries occur on San Juan Island; one at Limestone Point in section 18, T 36 N, R 3 W, and the other in section 34, T 36 N, R 3 W. A considerable tonnage of limestone still occurs at each of these locations.

Several thin strata of limestone occur in the Haro formation on the narrow arm which connects Davidson Head with the remainder of the island. These limestone beds are too small to be of any commercial value.


Although several large deposits of limestone occur on Orcas Island, none of them are being worked at the present time. Probably the largest undeveloped limestone ledge occurring on Orcas Island is found in section 2, T 36 N, R 2 W, and is commonly known as the McGraw-Kittinger limestone ledge. It is of scientific interest because it was formed largely by the Cariboniferous coral Lithostrotion. The chert beds which contain the limestone strata trend in a northeast and southwest direction and dip towards the southeast. The thickness of the limestone ledge varies from 25 to 40 feet, and it is exposed along the cliff for a distance of about 200 feet.

Across East Sound and apparently in line with the strike of the McGraw-Kittinger ledge, there is a deposit of limestone owned by the Tacoma Smelter. A considerable tonnage of limestone has already been quarried from this deposit but it has not been worked in recent years. This limestone layer outcrops at the shore of East Sound and rises almost vertically from the water's edge to a height of about 50 feet. It then bends abruptly so as to trend approximately N 40° E, and dips towards the southeast. It has been intruded by basic andesite which has since been converted into serpentine schist. The thickness of the limestone layer varies from 20 to 40 feet, and it may be traced, with an occasional small off-set, for a distance of about 300 feet.

Still farther to the northeast there are several small lenses which occur intermittently in the same general strike line. At a distance of about one and one-half miles to the northeast of the Tacoma Smelter deposit, there are three limestone lenses which vary from 15 to 30 feet in thickness. Several attempts have been made to develop these lenses but none of them have proved successful.

Along the shore of East Sound between the villages of Rosario and Olga there are several limestone lenses. One of these deposits (Plate XV-B), is so located that it might be developed with a profit even though its maximum thickness is only 20 feet. This deposit would permit only a limited amount of development for it dips towards the eastward into the precipitous side of Entrance Mountain. A considerable tonnage of limestone could be removed, however, without any danger of falling rocks.

Near the head of East Sound there are several deserted lime kilns with little or no limestone nearby. In one or two cases the kilns were never used, for the builders were not familiar with the typical pocket-like nature of the limestone lenses occurring in the cherts of the Orcas group, and had not previously tested out their deposit. In one instance, after the lime kiln had been completed, the whole limestone lens was blown out by one charge of powder.

The small limestone lenses occurring along the shore of East Sound to the south of Lookout Mountain, are cut by numerous igneous intrusions. None of these lenses are of any commercial importance.

Along the shore of West Sound, to the northeast of Sheep Island, there is a small though persistent limestone layer which trends northeasterly and dips towards the southeast. This stratum can be followed intermittently for several hundred yards. Another small limestone layer outcrops along the shore of West Sound to the southwest of Double Island. A very small lense of limestone outcrops on the east shore of Deer Harbor, about three-quarters of a mile north of Pole Pass.

At the southwest side of Orcas Knob, in section 31, T 37 N, R 2 W, there is a deposit of limestone of good quality belonging to J. Soderberg. This deposit was quarried to some extent several years ago, but unfortunately the limestone layer dips into the mountain face which rises vertically for several hundred feet.

Farther southward, in the same section, the quarries that were formerly operated by the Orcas Lime Company are apparently located on the same limestone layer. Although a considerable tonnage of limestone of good quality yet remains in the quarries, they had to be abandoned because of the height of the overhanging cliffs into which the limestone layer dips. The Orcas Lime Company operated two quarries in this locality, and a fairly modern lime burning plant is still located on the property. The limestone layer trends northeasterly parallel to the shore, and dips steeply towards the southeast into the face of the precipitous slopes which form the shore line.

About a mile to the southwest of the quarries belonging to the Orcas Lime Company, there is another deserted quarry which was formerly operated by the Imperial Lime Company. This quarry is apparently located on the same limestone layer that occurs along the shore to the northeastward. The limestone has been largely removed from this quarry, and the abandoned lime burning plant is now in a dilapidated condition. The limestone occurring in the quarry of the Imperial Lime Company has been intruded by igneous rocks.

Scattered lenses of limestone occur on Orcas Knob and along the shore to the northward, but these are all very small.

Along the northeast shore of Orcas Island, from Point Lawrence to the foot of Buck Mountain, there are scattered though persistent layers of limestone which occur in the rocks belonging to the Leech River group. At one time these Fusulina-bearing limestones were quarried and burned at a locality in section 22, T 37 N, R 1 W. The quarry was deserted partly because of the fact that the limestone was inferior in quality, and partly because of the cost of quarrying the beds which dip southward into the precipitous hill-sides.


Several small limestone lenses occur along the southwest shore of Shaw Island, and small scattered limestone deposits occur in association with the Orcas cherts in the west central part of the island. None of these deposits have any commercial importance.


A limestone layer with a thickness of 15 to 25 feet follows along the northwestern shore of Cliff Island. The limestone layer trends northeasterly and dips towards the southeast. It is associated with cherty rocks belonging to the Orcas group, but these have been intruded by dikes and sills of the Eagle Cliff porphyrite. About one-half of Cliff Island is composed of reddish colored ellipsoidal Eagle Cliff porphyrite. The limestone bed was quarried to some extent several years ago, but on account of the small tonnage present in the deposit it was abandoned.


At the southern margin of Crane Island, and almost directly in line with the strike of the bed occurring on Cliff Island, there is a small isolated lens of limestone. The margins of this limestone bed were burned to quicklime by the intrusions of ellipsoidal Eagle Cliff porphyrite, and although they have since been changed back into limestone, they still retain the cracked appearance peculiar to lumps of quicklime. This deposit is too small to be of any commercial importance.


A persistent limestone layer outcrops along the east shore of Jones Island, and trends northwesterly as far as the head of the large harbor which opens toward the northward. From this point the same or a similar bed of limestone trends westerly and outcrops along the west shore of the island. The maximum thickness of this layer of limestone is about 15 feet. It is associated with the Orcas cherts, but in many places it is bounded both above and below by igneous rocks. The limestone has been injured considerably by the intrusion of igneous rocks.


The southern end of O'Neal Island is crossed by a limestone layer which trends northeasterly. It has a maximum thickness of about 15 feet and a length of about 100 feet, and it is consequently too small to have any commercial value. In places it pinches down to a few inches in thickness.


On Henry Island, on the west side of Roche Harbor, there is a deserted limestone quarry and lime kiln belonging to the Roche Harbor Lime and Cement Company. A considerable amount of limestone still remains in this quarry. About midway along the west side of Henry Island there is a small isolated deposit of limestone which outcrops along the shore. Several small limestone lenses outcrop near the shores of Nelson Bay and also along the shores of the smaller bay to the northward.


The cement materials other than limestone occurring on the San Juan Islands are practically limited to the clays which are Pleistocene in age and glacial in origin.

The unmetamorphosed sediments of the Nanaimo series do not yield any materials suitable for the manufacture of cement. It is possible that some of the slates and argillites of the Leech River group could be used in the cement industry.

Due to the low percentage of magnesia in the limestones of the Orcas group they are well suited for the manufacture of cement. Many of the smaller limestone deposits have been silicified by igneous intrusions and they are consequently of no value for the manufacture of quicklime. This silicification, however, has not injured the limestones for the manufacture of Port land cement.


On the Kimple estate, in section 21, T 37 N, R 2 W, there is a large deposit of glacial clay of good quality. A small brick manufacturing plant has recently been established in this locality, and a wharf or landing is being constructed at Kimple Bay.

The clay is uniform and quite plastic, and on burning it turns to a light buff color. The bricks are light in weight and they hold their shape well. Their surfaces are smooth and pleasing in appearance. The future outlook for this newly established industry is very bright.

A small deposit of plastic clay is located in the lowland to the north of East Sound.

In section 21, T 37 N, R 1 W, there is a deposit of clay and a brick-yard was at one time located there. The clay is light yellowish-gray in color and it possesses a good plasticity. Its chemical composition is as follows:42

42Shedd, Solon, Cement Materials and Industry in the State of Washington: Wash. Geol. Survey, Bull. 4, p. 206, 1913.

Loss on ignition4.74%

A. A. Hammer, Analyst.
PLATE XXII. Above: Fedspar rock deposit at Deer Harbor, Orcas Island. Below: Feldspar rock deposit at Deer Harbor, Orcas Island.


A deposit of plastic glacial clay occurs at the head of Westcott Bay, almost adjoining the lime works of the Roche Harbor Lime and Cement Company. Small scattered clay beds occur throughout the San Juan Valley.


A large part of the north end of Lopez Island is covered with glacial sediments which include a layer of clay from 15 to 30 feet thick. This clay is not very plastic for in places it grades off into sandy clays.


Probably the largest deposits of plastic clay in the map-area are located on Guemes Island. A well defined layer of lay with a maximum thickness of 30 feet covers the greater part of the island. A large part of this clay is plastic but nothing is known about its burning qualities.


Near the village of Friday Harbor, in section 13, T 35 N, R 3 W, there is a large deposit of coarse sand and gravel. The material extends from Friday Harbor to Griffin Bay and constitutes what is known as Bald Hill. It was deposited by the last retreating glacier, being temporarily a part of the terminal moraine.

During the year of 1924, bunkers were constructed on the shore of Friday Harbor so that barges are now able to load by gravity. Salt water is pumped up to the gravel pit to be used for washing down and sorting the sand and gravel. Bald Hill contains an enormous amount of coarse sand and gravel.


On the west shore of Deer Harbor in section 7, T 36 N, R 2 W, there is a large deposit of feldspar rock belonging to A. D. Tift. Farther westward the same material occurs as a network intermingled with other types of intrusions which make up the injection breccia of the Turtleback complex. Smaller intrusions of white feldspar and quartz occur on the west shore of West Sound, in section 8, T 36 N, R 2 W. They are also found on Turtleback Range.

At the time of its discovery the Deer Harbor feldspar rock deposit was mistaken for limestone. When it was found that it would not make quicklime, the owners sent away samples of the rock for examination and determination. The samples were incorrectly determined as a silica-bearing rock suitable for the manufacture of glass. Several attempts were made to utilize this material in the glass industry. Trial lots were tested on a small scale at Anacortes, and again at Everett, Washington. None of the enterprises met with success though it was not fully realized that the rock was unsuited for the manufacture of glass.

During the summer of 1922, the writer obtained samples of the feldspar rock, known locally as the glass rock, and discovered that it was composed largely of soda-bearing feldspar. Burning tests conducted by the Ceramics Department of the University of Washington showed that it fused at Seger cone No. 8-1/2 and produced a pure white glassy glaze. It therefore met with the burning requirements of the desired grade of feldspar, and subsequent tests showed that it produced excellent results as an ingredient in the manufacture of the finest grade of porcelain.

The Deer Harbor feldspar rock is composed almost entirely of feldspar and quartz. The bulk of the feldspar is soda orthoclase together with lesser amounts of albite and orthoclase. An occasional small flake of muscovite is the chief accessory mineral. Exceedingly small quantities of magnetite, zircon, tourmaline, titanite, and apatite are sometimes found in the rock. The chief secondary minerals are kaolinite and sericite.

Along the west shore of Deer Harbor there are four injected masses of the feldspar rock which outcrop along a cliff about 75 feet high. They were intruded as pegmatites into the injection breccia which makes up the Turtleback complex. Some of the dikes trend in a northeast and southwest direction and dip towards the northwest at an angle of about 40 degrees. The usual occurrence of the feldspar rock is in the form of irregular masses.

The largest and most northern body of feldspar rock is stained with ferric oxide derived from the alteration of biotite. It is a coarse-grained pegmatite with individual crystals of quartz and feldspar measuring about half an inch in diameter. The thickness of this deposit as it outcrops along the shore is about 60 feet.

The remaining three deposits outcropping along the shore of Deer Harbor are pure white in color. The most southern of these occurs in the form of a dike which is about 25 feet thick at the water's edge, but is not exposed at the top of the cliff. This is the smallest of the four deposits, but the quality of the rock is excellent.

Between these two deposits there are two other large ones of high quality. The latter are very irregular in shape and they blend with each other in places. They may be followed inland with certainty for about 300 feet from the edge of the cliff, but their size diminishes rapidly. The larger of these deposits averages about 45 feet in thickness, and the smaller one is about 35 feet thick. Where the two deposits are fused together they measure more than 300 feet along the face of the cliff. In places they are intermingled with irregular masses of lamprophyric material.

The mineral composition of the deposits of feldspar rock is not constant even within a single deposit. Some portions are relatively high in quartz, others show the eutectic mixture of quartz and feldspar in the formation of a graphic intergrowth of these two minerals, still others are composed largely of feldspar in excess of the eutectic ratio.

Although the feldspar rock is usually medium to fine-grained, it is distinctly pegmatitic in character. It does not show the granular or sugary texture typical of an aplite. The feldspars have suffered considerably from kaolinization so that the multiple twinning of the albite is partly concealed. For this reason it is difficult to determine the original percentages of albite and soda orthoclase.

The average chemical composition of the Deer Harbor feldspar rock is as follows:



(Analysis made in 1924 by Carl Woods of the United States Bureau of Mines, Seattle, Wash.)

The feldspar rock fuses at Seger cone No. 8-1/2 or about 1300° C., and it burns to a pure white color. It has been thoroughly tested by the Ceramics Department of the University of Washington, and it proves to be excellent as an ingredient in the manufacture of high grade porcelain.

The Deer Harbor feldspar deposit is situated in an ideal location for transportation, for the shore slopes abruptly to a depth of about 40 feet below sea-level, and barges could be loaded with the minimum of expense.


Considerable prospecting for coal has been done in the rocks of the Nanaimo series. Several years ago the Northwest Construction Company of Seattle put down a two-inch diamond drill hole on Waldron Island. The hole is located on the property of Ethan Allan, near the shore of Mail Bay. The location selected for the drilling was very unfortunate, for the greater part of the rock-section was already well exposed along the shore. The writer was not able to locate the log of the well, which was nearly 1500 feet deep, but it is said that small amounts of coal were encountered at three different horizons. The greater part of the core of the well is still located on the property of Ethan Allan.

The lignitic leaf-bearing shales occurring on Orcas Island to the south of Point Doughty have been prospected for coal seams, but nothing larger than pockets have been found.

In 1924 a portion of Sucia Island was taken out as a coal claim by Henry Parrott of Seattle. The stratigraphic section on the Sucia Islands is similar to that occurring in the coal measures at Nanaimo, British Columbia, and the erosional valleys with the bedrock concealed by mantle materials are consequently worth investigating.

The Leech River sediments occurring along the northeast side of Orcas Island have been prospected to some extent for coal. A number of small seams of semianthracite have been discovered but no deposits of commercial importance have been opened up as yet. No coal from this source has ever been shipped but the local blacksmiths have used it in their forges. These deposits of coal are of Pennsylvanian age.


The dunite dikes of the Fidalgo formation occurring on Cypress Island contain variable amounts of chromite. Sometimes the schlieren-like masses of chromite are sufficiently large to make their exploitation profitable. The deposits are scattered throughout the whole island, but the largest pockets of chromite discovered up to the present time have been located well up on the slopes of Cypress Dome.

In 1922 the Cypress Island chromite deposits were examined by Pardee, whose report43 is freely quoted in this description.

43Pardee, J. T., Chromite Ores in Washington: U. S. Geol. Survey, Bull. 725, pp. 61-65, 1922.

The total production of chromite to date is 200 tons, most of Which contained between 45 and 50 per cent of chromic oxide. The known deposits still contain several thousand tons of material averaging between 10 and 25 per cent of chromic oxide.

The largest ore body is located on the Ready Cash claim on the steep western slope of Cypress Dome. The claim is located about 1100 feet above sea-level, and about three-quarters of a mile from the shore. It was developed by an open cut 10 feet wide, 15 feet long, and six feet deep, from which about 25 tons of ore were mined. In 1918 the Cypress Chrome Company extended this mine and extracted 50 tons of chromite. Ore from the Ready Cash claim consists of coarse granular chromite intergrown with the rose-red chrome chlorite, kotschubeite, a chromium-bearing limonite, and a light green chromium-bearing variety of hornblende.

On the shore of Cypress Lake there are two claims that have been prospected for chromite. Ore taken from the Last Chance claim at the south end of the lake carried about 25 per cent of chromium oxide.

Numerous other deposits of chromite occur on the island but their size is small. The chromite occurs in association with the dunite dikes and in no instance was there any notable concentration of chromite in the original stock-like intrusions. No concentrations of chromite were found on the other islands composed of the Fidalgo formation.


Some of the Cretaceous sandstones occurring in the Nanaimo series are suitable for building purposes. Rocks of this kind occur on Sucia Island, Matia Islands, Waldron Island, and to a certain extent on Stuart and Johns islands.

On Sucia Island the coarse to medium-grained buff-colored sandstone occurring on the north side of Fossil Bay could be utilized for building purposes. At one time a quarry was operated on this sandstone formation and the rock was used in Seattle for paving-blocks. The sandstone proved to be too soft for such a purpose and the quarry was consequently abandoned. A certain amount of this sandstone is suitable for the manufacture of grindstones. All of the rock in this formation is easy to extract because it has two good partings at right angles to each other.

A considerable amount of sandstone has been quarried on Waldron Island and shaped into small rectangular blocks. A large amount of this material has been used in the construction of the jetties at the mouth of the Columbia River. The quarries are located on the east side of Point Disney.

Sandstone has been quarried at Reid Harbor on Stuart Island. In general the sandstones occurring on Stuart Island and Johns Island are not as easily accessible as those on Sucia Island.

Some of the graywackes and indurated sandstones of the Haro formation occurring to the south of Davidson Head might be used for building purposes.

The graywackes occurring in the sediments of the Leech River group at Humphreys Head on Lopez Island have been quarried to some extent.

The igneous rocks occurring on the San Juan Islands are not suitable for building purposes.


The chief supplies of fresh water occurring in the San Juan Island map-area are found in the large and elevated lakes on Orcas, Blakeley, and San Juan Islands.

On Orcas Island, Mountain Lake with an elevation of 915 feet, and Cascade Lake with an elevation of 350 feet, are capable of supplying a moderately large quantity of water at all seasons of the year. Buck Lake, Killebrews Lake, and the Twin Lakes also contain a considerable volume of water. The large bogs occurring on Mount Constitution Range and in other localities in the map-area are capable of retaining a remarkably large volume of water. The water derived from the relatively heavy precipitation which falls on Mount Constitution Range is naturally conserved so efficiently that numerous streams issue from all sides of the range at all seasons of the year. Orcas Island is abundantly supplied with water.

On Blakeley Island, Thatcher Lake with an elevation of 188 feet, and Blakeley Lake with an elevation of 374 feet, are capable of supplying a considerable volume of water.

San Juan Island has three lakes of moderate size, Sportsmans Lake, Trout Lake, and Egg Lake. The water resources of San Juan Island are somewhat limited excepting in the northern portion where the rocks of the Orcas group are encountered. The underground water supply is found especially in the fractured cherts of the Orcas group, and artesian wells have resulted on Shaw Island in some instances when the overlying Leech River sediments were penetrated.

Lopez Lake, with an elevation of 91 feet, is the only body of surface water occurring on Lopez Island. Water can be readily obtained, however, by penetrating certain impervious strata in the glacial sediments which cover the greater part of the island.

Several small lakes occur on Cypress Island but their combined volume of water is very small.

The smaller islands of the San Juan group are occasionally so lacking in fresh water that a species of prickly cactus may be found growing on them. It is very remarkable, however, that some of the small, bare, rocky islands which are isolated from the others by exceedingly deep channels, have an abundance of freshwater at a depth of 40 or 50 feet below the surface.

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Last Updated: 28-Mar-2006