University of Washington Publications in Geology The Geology of the San Juan Islands

DRAINAGE

The streams occurring on the various islands of the San Juan group are few in number and are all quite small. They usually follow courses that were determined by fault or fracture zones which have been subjected to glacial erosion and modification.

ISLANDS

ORCAS ISLAND

The large bogs occurring on Mount Constitution Range retain a large part of the rain falling on this area during the wet season. This water is delivered to the sea by streams radiating in every direction from the center of the Range. The bogs are so efficient in storing the rain water that many of the streams vary but little in size during the different seasons of the year.

Mountain Lake, with an elevation of 915 feet, derives a large part of its water from bogs which occur on Mount Constitution Range. An artificial dam at the south end of the lake has raised the water level to such an extent that many of the trees occurring near the original shores of the lake have been partly submerged.

Twin Lakes, with an elevation of 1100 feet, drain both to the northward directly into the sea, and also to the southward where a small stream issuing from them empties into Mountain Lake. A large stream issues from the south end of Mountain Lake. By means of a series of waterfalls and rapids its drops about 600 feet within a distance of one and one-half miles. It is joined by another stream issuing from Cascade Lake, and the combined streams empty into the waters of East Sound at the village of Olga. The natural courses these streams have been considerably changed by water-flumes and other artificial means.

Cascade Lake, with an elevation of 350 feet, drains to the westward directly into Cascade Bay. This water is now used to furnish power for a large electric generating plant.

A small stream drains southward from the slopes of Mount Constitution Range and empties into Cascade Lake. Another small stream which issued from the western slopes of this range empties into East Sound near Giffin Park.

Small intermittent streams issue from Buck Lake and from Killebrews Lake. A small intermittent stream flows into the waters of West Sound at its northern extremity. About half a mile to the south of Point Doughty there is a small continuous stream which issues from water seepages along the slopes of the adjoining hill.

PLATE XII. Figs. 1 & 2. Phylloceras spiedenensis n. sp. Type specimen. Fig. 3. Holodiscus ?? stantoni n. sp. Paratype. Figs. 4 & 5. Holodiscus ?? stantoni n. sp. Type speciments. Fig. 6. lima spiedenensis n. sp. Type specimen. Fig. 7. Pleuromya typa n. sp. Type specimen. Figs. 8 & 9. picuromya thor n. sp. Type specimen. Fig. 10. Halobia sp. Halobia impressions in a carbonaceous shale from the Haro formation.

SAN JUAN ISLAND

There are no continuous streams on San Juan Island. During the wet season a small stream follows the bottom of the San Juan Valley and empties into False Bay.

Sportsmans Lake, the largest lake on the island, is drained by a small intermittent stream which flows eastward and empties into San Juan Channel. Egg Lake has no outlet though it is connected with Sportsmans Lake by a narrow swampy passage.

The village of Friday Harbor is supplied with water derived from Trout Lake nearly five miles away. Trout Lake has no outlet which reaches the sea.

A small intermittent stream enters the eastern corner of Westcott Bay. Another intermittent stream follows the valley to the southeast of Sportsmans Lake and empties into Friday Harbor.

LOPEZ ISLAND

Lopez Lake, with an elevation of 91 feet, is drained by a small stream which empties into Swifts Bay at the village of Port Stanley.

A small intermittent stream which flows southwesterly empties into the east side of Davis Bay, to the north of Nigger Head.

BLAKELEY ISLAND

A small stream issues from Blakeley Lake and flows southeasterly. Although it flows in the direction of Thatcher Lake it sinks into the ground before reaching that point. A large stream issues from Thatcher Lake and empties into Thatcher Harbor. This stream has a very steep gradient and the water is used to supply power for a saw-mill at Thatcher post office.

CYPRESS ISLAND

A small intermittent stream which originates in the swampy region to the south of Cypress Lake empties into Strawberry Bay.