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Geology and Earth Resources Division Bulletin No. 72

Washington Coastal Geology between the Hoh and Quillayute Rivers



Offshore islets, rocks, and reefs extending intermittently from Toleak Point to and including the Giants Graveyard (front cover photo) are composed chiefly of sandstone, but, in places, are stratified with fine-grained siltstone. This stratification reveals that the rocks are steeply tilted and complexly folded with a structural trend striking in a northerly direction somewhat parallel to the coastline. Intense folding and discontinuous or offset bedding resulting from faulting indicates that considerable crustal force and stress have been applied to these rocks. Although these sedimentary rocks generally constitute a coherent sequence of strata, they have nevertheless been greatly rearranged from their original horizontal position. Well-stratified sandstone and siltstone are particularly well exposed at Strawberry Point (fig. 2). They strike northerly and dip steeply to the east. Furthermore, on the basis of sedimentary features preserved in these rocks, it can be determined that the sequence has been rotated beyond vertical to an overturned position with the original bottom side of each bed now facing upward. Several different sedimentary features can be seen in these rocks. However, the most apparent feature is GRADED BEDDING or the grading of the size of sand grains from coarse to fine in a single sandstone bed (fig. 50). The top of each bed is always in the direction of the finest grains. At Strawberry Point that direction of grading in the steeply tilted beds is toward the west and slightly downward.

GRADED BEDDING, shown diagrammatically in cross section, is a process of sedimentation that can be used to determine the original top-bottom orientation of an ancient sedimentary sequence seen today as upturned sedimentary rock strata (fig. 50).

Melange rock debris, similar to that exposed much of the way between Hoh Head and Goodman Creek, is also almost continuously exposed in the bluffs between the north end of the Goodman Creek trail and Taylor Point. Countless numbers of large and small sandstone blocks are intermixed in a finer grained siltstone and claystone matrix. Landslide areas are numerous for several miles along essentially continuous outcrop. Although the bluff in the cove between Toleak Point and Strawberry Point is mostly vegetated, it too is probably underlain by melange rocks.

Small natural petroleum seeps are common along the Washington coast. Most are associated with melange rocks such as those exposed along this few miles of outcrop. A strong petroleum odor usually can be detected emanating from the cliffs of melange rocks in the area immediately south of the mouth of Jackson Creek.

Deposits of the Pleistocene Epoch are particularly well exposed in the bluffs between Scott's Bluff and Taylor Point, where they form a cap on the melange bedrock. Landslides are prevalent in this area and have exposed the overlying deposits in SCARPS formed behind the landslide debris. In some places Pleistocene material has been carried to the beach as part of the debris slide (fig. 51). Many of the younger deposits consist of laminated silt with carbonized plant and woody material varying in size from branches to logs. These highly organic materials represent deposition of an ancient fresh-water pond or swamp. Although radiocarbon dates are not known from this particular deposit, its stratigraphic position indicates that it represents the latest deposition prior to that of the overlying buff-colored wind blown deposits. The latter materials are also well exposed here and are thought to have been deposited approximately 8,000 years ago (see Age dating of Ice age events, Part I).

A TYPICAL LANDSLIDE commonly occurs where melange rocks are present. Overlying Pleistocene materials north of Scott's Bluff make up most of the debris of this landslide. Undisturbed Pleistocene deposits are visible in the scarp behind the debris (fig. 51).

Although the geology of the area extending from a mile south of Toleak Point to Taylor Point appears somewhat monotonous, it nevertheless is an ideal representation of the rock type and structural style that dominates in much of the coastal region of the Olympic Peninsula. As between the Hoh River and Goodman Creek, tectonic melange rocks are exposed in the major part of the bluffs between Toleak Point and Taylor Point. Inland these rocks form a zone approximately a mile wide extending northward generally up the Scott Creek valley (fig. 25). Also, as in the coastal area to the south, this zone is thought to be a large segment of a major fault zone where rock debris has resulted from the thrusting of one segment of the earth's crust beneath another (Rau, 1979). The sandstone and conglomerate beds in the Goodman Creek area and northward into an inland area constitute the upper crustal plate. The offshore rocks extending from the vicinity of Toleak Point to and including the Giants Graveyard area are believed to be part of the contorted strata of the plate beneath. Because this and other coastal fault zones cover relatively wide areas, they are believed to extend downward between plates at a low angle relative to the earth's surface.


Bluffs of melange rocks end abruptly at the southeast side of Taylor Point. This major headland (fig. 52) and its offshore stacks (fig. 53) are composed largely of conglomerate and some massive sandstone—rocks similar to those exposed in the vicinity of Goodman Creek. Taylor Point rocks are believed to constitute a small segment of a much larger part of the earth's crust. They represent some of the strata that are referred to as HOH ROCK SEDIMENTARY SEQUENCES (see Part I). The abrupt change from melange rock to a sequence of sedimentary rocks both on the south and north sides of Taylor Point reflects the result of complex northeast strike slip faulting. Strata of Taylor Point have moved southwestwardly relative to adjacent rocks (fig. 25). The contact of these rocks with melange rocks on both the south side and north side of Taylor Point represents the trace of these faults. Although the rock strata of Taylor Point are structurally complex, generally they form a SYNCLINAL (downwarp) structure with an axis of folding that trends northwestwardly. A cross-sectional view of this structural feature can be seen from offshore.

SOUTHEAST SIDE OF TAYLOR POINT. The sandstones and conglomerates of Taylor Point are believed to constitute a faulted segment of a much larger part of the earth's crust (fig. 52).

AN EROSIONAL REMNANT of massive sandstone off Taylor Point. The notched-like area just above high-tide level has resulted from more rapid weathering where the rock surface is repeatedly dried and then moistened by waves and sea spray (fig. 53).

Ice age or Pleistocene events are also represented on Taylor Point. The ancient wave-cut terrace, the trace of which is visible in many places along the coast, stands some 150 feet above present-day sea level at Taylor Point (fig. 54). It marks the nearly horizontal contact between conglomerate or sandstone Hoh bedrock and the overlying unconsolidated silts, sands, and gravels of the Pleistocene Epoch. Particularly good observations of these deposits can be made along the north end of the trail over Taylor Point. The sequence is well exposed in the area where the trail first breaks out of the woods and begins its descent from the top of the cliff to Third Beach. Looking southward, the entire sequence can be viewed (fig. 15). The uppermost 8- to 10-foot thickness of buff-colored sand and silt is believed to be windblown material deposited some 8,000 years ago and represents essentially the latest Pleistocene event in this area. These deposits grade downward into a 10- to 15-foot thickness of well-stratified sand and gravel. They rest on the old wave-cut terrace that was carved on sandstone and conglomerate Hoh bedrock. The trail descends northward along this same sequence of deposits, where it continues downward across the wave-cut terrace and along excellent outcrops and large boulders of Hoh conglomerate and massive sandstone.

ICE AGE DEPOSITS rest on an elevated wave-cut terrace at Taylor Point (fig. 54).

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Last Updated: 28-Mar-2006