Hydrology
Scotts Creek is 30 miles (48 km) long. It is the largest tributary of Clear Lake, contributing about 24% of the streamflow to the lake with a watershed that covers 23% of the Clear Lake basin. Clear Lake drains to the east via Cache Creek to the Sacramento River.
The course of Scotts Creek resembles a letter "S" with its vertical axis tilted 45° clockwise. The creek forms to the south of Cow Mountain, and then runs southeast to its junction with the creek's South Fork. It turns east and then northeast past Lakeport, then flows northwest through the fertile Scotts Valley up to the outlet from the Blue Lakes. From this point it turns east and flows through Tule Lake towards Upper Lake, then turns southeast and joins Middle Creek. The combined stream flows south through Rodman Slough into Clear Lake. Various man-made barriers block the passage of fish in the river. The total flow is estimated at 115,116 acre⋅ft (141,993,000 m3) per year.
Tule Lake is a seasonal lake that forms in the winter when Scotts Creek overflows its banks. The lake floods every year except when there is a severe drought. It drains along Scotts Creek into Rodman Slough, which flows into Clear Lake. There is only a slight change in elevation along Scotts Creek between the Blue Lakes, Tule Lake and Clear Lake, and the channel is shallow and prone to flooding. Parts of Bachelor Valley may be flooded when Tule Lake backs up and passed through the culverts under highway 20. Tule Lake serves to reduce sedimentation in Clear Lake, because the high flows of Scotts Creek spread out in the lake, slow down and drop their sediment.
Geological changes
Clear Lake formed about 600,000 years ago as the land in the region began to subside when the Clear Lake Volcanic Field erupted. Its basin continues to move downward, while sedimentation keeps it shallow. The Clear Lake basin lies between the watersheds of the Sacramento River and the Russian River. When it was formed it drained east into the Sacramento Valley.
About 200,000 years ago the Clear Lake Volcanic Field blocked the lake's outlet. The lake rose until it found a new outlet, draining west through the Blue Lakes into Cold Creek and the Russian River. Clear Lake was almost 300 feet (91 m) higher than it is today, and Scotts Creek flowed into the lake from the west near where Lakeport is today. It formed a large delta there, which deposited the Lakeport ridge.
At some time in the last 10,000 years a landslide at the west end of the Blue Lakes blocked Clear Lake's outlet to the Russian River watershed. The lake rose again, and created its present outlet via Cache Creek to the Sacramento River. Cache Creek began eroding upstream to Clear Lake, and when it reached the lake the outflow along Cache Creek quickly eroded a channel through soft sediments. The lake dropped almost 300 feet (91 m) as a result.
Scotts Creek eroded through its old delta to carve out Scotts Valley behind the Lakeport Ridge. A landslide to the west of Blue Lakes blocked Scott Creeks and created a lake in Scotts Valley. Eventually the creek broke through to join the Upper Lake drainage to Clear Lake and drained the Scotts Valley lake.
Human presence
Scotts Valley, which slopes to the north with elevations from 1,460 to 1,400 feet (450 to 430 m) is an important agricultural center, and Bachelor Valley, Tule Lake and Benmore Valley are also used for agriculture. California State Route 20 runs across the northern part of the watershed from east to west. There are no towns in the watershed.
European presence in the watershed began when the brothers Salvador Vallejo and Juan Antonio Vallego established a cattle ranch covering a land grant that covered Upper Lake, Bachelor Valley, Scotts Valley, and Big Valley. American farmers started to settle the area after California became a state in 1850. They planted crops such as grains, potatoes, grapes and orchard crops, but because of transportation difficulties relied on cattle and sheep for income. Grazing quickly led to the native perennial bunchgrasses being replaced by an annual grassland with grasses of European origin. Fire was also used to convert brush to grasslands.
Visitors from the San Francisco Bay Area and the Central Valley came for health or to vacation at the mineral springs resorts in Lake County. The Witter Springs resort opened on the west side of Bachelor Valley soon after the springs were discovered in 1870. The Pearson Springs Hotel had opened by 1879, later to become the Saratoga Springs resort. The Blue Lakes Hotel opened in 1870 on the west end of upper Blue Lake where the Pine Acres Resort is today.
Commercial agriculture expanded in the early 1900s as better roads and railways made transport of produce more practical. In 1944 important crops in Scotts Valley included pears, walnuts, hop's and green beans, which were mainly grown in land reclaimed from the former Tule Lake. There were about 800 dairy cows around the Upper Lake and Scotts Valley in 1944. Since then there has been a steady decline in fruit and nut production.
Sedimentation in Clear Lake increased greatly after 1927 due to use of heavy earth-moving equipment to build roads, reclaim wetlands, conduct open-pit mining and mine gravel from the streams. The headwaters of Scotts Creek on South Cow Mountain were severely burned in 2018 by the Mendocino Complex Fire, which may have increased erosion and the flow of sediments and dissolved nutrients into the Clear Lake.
The Sacramento River is the principal river of Northern California in the United States and is the largest river in California. Rising in the Klamath Mountains, the river flows south for 400 miles (640 km) before reaching the Sacramento–San Joaquin River Delta and San Francisco Bay. The river drains about 26,500 square miles (69,000 km2) in 19 California counties, mostly within the fertile agricultural region bounded by the Coast Ranges and Sierra Nevada known as the Sacramento Valley, but also extending as far as the volcanic plateaus of Northeastern California. Historically, its watershed has reached as far north as south-central Oregon where the now, primarily, endorheic (closed) Goose Lake rarely experiences southerly outflow into the Pit River, the most northerly tributary of the Sacramento.
Lake County is a county located in the north central portion of the U.S. state of California. As of the 2020 census, the population was 68,163. The county seat is Lakeport. The county takes its name from Clear Lake, the dominant geographic feature in the county and the largest non-extinct natural lake wholly within California.
Clear Lake is a natural freshwater lake in Lake County in the U.S. state of California, north of Napa County and San Francisco. It is the largest natural freshwater lake wholly within the state, with 68 square miles (180 km2) of surface area. At an age of 0.5 million years, it is the oldest lake in North America. It is the latest lake to occupy a site with a history of lakes stretching back at least 2,500,000 years.
The Pit River is a major river draining from northeastern California into the state's Central Valley. The Pit, the Klamath and the Columbia are the only three rivers in the U.S. that cross the Cascade Range.
The Feather River is the principal tributary of the Sacramento River, in the Sacramento Valley of Northern California. The river's main stem is about 73 miles (117 km) long. Its length to its most distant headwater tributary is just over 210 miles (340 km). The main stem Feather River begins in Lake Oroville, where its four long tributary forks join—the South Fork, Middle Fork, North Fork, and West Branch Feather Rivers. These and other tributaries drain part of the northern Sierra Nevada, and the extreme southern Cascades, as well as a small portion of the Sacramento Valley. The total drainage basin is about 6,200 square miles (16,000 km2), with approximately 3,604 square miles (9,330 km2) above Lake Oroville.
Coyote Creek is a river that flows through the Santa Clara Valley in Northern California. Its source is on Mount Sizer, in the mountains east of Morgan Hill. It eventually flows into Anderson Lake in Morgan Hill and then northwards through Coyote Valley to San Jose, where it empties into San Francisco Bay.
Cache Creek is an 87-mile-long (140 km) stream in Lake, Colusa and Yolo counties, California.
East Fork Russian River is a 15 mi (24 km) long tributary of the Russian River in Mendocino County, California artificially connected to the Eel River via an interbasin diversion at the Potter Valley Project hydroelectric facility. It forms in the north of Potter Valley, flows south through this valley, then southwest through a mountain pass to Lake Mendocino, an artificial reservoir that empties into Russian River. At one time Clear Lake to the east drained through Cold Creek then along the lower part of East Fork Russian River through Coyote Valley to the Russian River proper. A few hundred years ago a massive landslide blocked this channel, and Clear Lake found a new outlet to the Sacramento River.
Stony Creek is a 73.5-mile (118.3 km)-long tributary of the Sacramento River in Northern California. It drains a watershed of more than 700 square miles (1,800 km2) on the west side of the Sacramento Valley in Glenn, Colusa, Lake and Tehama Counties.
Cottonwood Creek is a major stream and tributary of the Sacramento River in Northern California. About 68 miles (109 km) long measured to its uppermost tributaries, the creek drains a large rural area bounded by the crest of the Coast Ranges, traversing the northwestern Sacramento Valley before emptying into the Sacramento River near the town of Cottonwood. It defines the boundary of Shasta and Tehama counties for its entire length. Because Cottonwood Creek is the largest undammed tributary of the Sacramento River, it is known for its Chinook salmon and steelhead runs.
Kelsey Creek is a watercourse in Lake County, California, United States, that feeds Clear Lake from the south. The watershed was forest-covered. In the lower parts it has been converted to farmland and for urban use. Higher up the forests have been cleared, regrown and cleared again. The northern part of the creek flows through a geothermal field that feeds power plants and hot springs. The wooded Cobb area in the higher part of the watershed holds resorts and resort communities, some dating to the 1850s.
Cow Mountain is a ridge in the Mayacamas Mountains in Lake County, California, and Mendocino County, California. It is home to two large recreation areas. One is closed to off-road vehicles and the other is not. Erosion from the mountain, caused in part by human land use, contributes sediment and nutrients to Clear Lake.
Cow Mountain Ridge is a ridge in Lake County, California, and Mendocino County, California. It joins Cow Mountain from the south.
Cold Creek is a river of Mendocino County, California, a tributary of East Fork Russian River. In the past it may have connected Clear Lake to the Russian River before this route was blocked by a large landslide and Clear Lake began to drain into the Sacramento River watershed.
The Blue Lakes are a string of two or three lakes in Lake County, California, set in a deep canyon. At one time they seem to have been in the Russian River watershed, but a recent geological upheaval cut them off from that basin and they now drain via Scotts Creek into Clear Lake in the Sacramento River basin. In the 19th and early 20th centuries there were several resorts around the lakes. Their waters have been highly altered by human activity and most of their native fish are lost, but they have a healthy population of largemouth bass.
Tule Lake is a seasonal lake in Lake County, California. It is named after the edible bullrushes, or tules, that used to surround the lake. These have been cleared and the lake partly drained to support agriculture, but it still floods every winter. In summer it is used for growing wild rice and grazing cattle. There have been proposals to restore the lake to its original wetlands condition.
Rodman Slough is a wetland that drains into Clear Lake in Lake County, California. It provides an important habitat for fish, amphibians, birds and other wildlife. It is fed by Scotts Creek and Middle Creek, which contribute about 70% of the sediment and nutrients that cause algae problems in Clear Lake. The slough is the remnant of a much larger area of wetlands and open water that extended from Tule Lake to the northeast through a wide area of land north and east of the present slough that was drained for farmland. Since 1978 there have been proposals to restore large parts of the former wetlands, and much of the funding has been approved, but progress has been slow.
Middle Creek is a creek that drains through Rodman Slough into Clear Lake in Lake County, California. It supplies 21% of the streamflow to Clear Lake. The watershed vegetation has been drastically modified by European settlers through sheep and cattle grazing, logging and farming in the valley floors. The creek once flowed through extensive wetlands at its mouth, but these were mainly drained to create farmland, apart from Rodman Slough on the west side. There are now projects to restore the drained land to its original condition.
Rivers and creeks in Lake County, California are listed below by river basin and alphabetically. Unless otherwise stated, the information is taken from the Geographic Names Information System maintained by the United States Geological Survey. Coordinates, elevations and lengths from this source are approximate.
