The Trinity River (Yurok: Hoopa or Hupa; Hupa: hun') is a major river in northwestern California in the United States and is the principal tributary of the Klamath River. The Trinity flows for through the Klamath Mountains and Coast Ranges, with a watershed area of nearly in Trinity and Humboldt Counties. Designated a National Wild and Scenic River, along most of its course the Trinity flows swiftly through tight canyons and mountain meadows.
The river is known for its once prolific runs of anadromous fish, notably Chinook salmon and steelhead, which sustained Native American tribes for thousands of years. Due to its remoteness, the Trinity did not feature prominently in the early European colonization of California, but the gold rush in the mid-1800s brought thousands of gold seekers to the area. The river was named by Major Pierson B. Reading who, upon reaching the river in 1848, mistakenly believed it to flow into the Pacific Ocean at Trinidad Bay. During and after the gold rush, the influx of settlers and miners into the Trinity River country led to conflict with indigenous tribes, many of which saw severe depopulation due to fighting and foreign diseases. In the following decades logging and ranching, combined with mining runoff, significantly changed the river's ecosystem and led to the decline of its fish populations.
The Trinity River is an important water source for irrigation and hydroelectricity generation, as well as a major center of recreational activities such as gold panning, fishing and whitewater rafting. Since 1964 the Trinity River has been dammed to create Trinity Lake, the third largest man-made lake in the state. As much as 90 percent of the upper Trinity River watershed was diverted for agriculture in the Central Valley. In 1991 environmental regulations were enacted, requiring a greater release of water to the Trinity River in order to protect fish. However, the use of Trinity River water remains a contentious issue, especially in years of drought.
Course
The Trinity River begins deep in the Scott Mountains, in Trinity County, at the confluence of High Camp Creek and Chilcoot Creek. It flows south through a deep valley between the Trinity Mountains to the east as well as the Salmon Mountains/Trinity Alps and Scott Mountains to the west. The river picks up its first large tributary called Bear Creek near a series of large spring filled meadows roughly one mile from the headwaters. The short but steep Bull Creek comes in just shortly down stream from the West. Cedar Creek is the next major tributary that meets from the East. The river continues to flow in a Southwestern direction picking up numerous tributaries before entering Trinity Lake, a large reservoir created by the Trinity Dam. These tributaries include Picayunne Creek, Nyott Creek, and Sherer Creek, Sunflower Creek, and more. Coffee Creek, the Little Trinity River, Tangle Blue Creek, and Eagle Creek are the largest tributaries above the lake. East Fork and Stuart Fork of the Trinity River also flow into the reservoir along with many other tributaries. Just below Trinity Dam is the smaller Lewiston Dam, which diverts part of the Trinity River through a hydroelectric plant to the Sacramento River Basin as part of the Central Valley Project, providing irrigation water to California's Central Valley.
Below Lewiston Dam the Trinity River passes the towns of Lewiston and receives another large tributary named Grass Valley Creek, before passing Douglas City and turns west, passing within a few miles of Weaverville, the seat of Trinity County and the main population center of the area. It then turns northwest and receives Browns Creek, passes Junction City, and receives Canyon Creek and the North Fork Trinity River at Helena. Further west it passes the former mining settlement of Big Bar and receives Price Creek. It then enters a deep gorge, which provides the route for Highway 299, the principal road connecting Redding to the Humboldt Bay area. At Burnt Ranch it receives the New River from the north. At Salyer the South Fork, its main tributary, enters from the south, nearly doubling the flow.
At the confluence of the South Fork, the Trinity River turns sharply north, entering Humboldt County. It flows through the wider steep-sided namesake valley of the Hoopa Valley Reservation, past the towns of Willow Creek and Hoopa. It joins the Klamath River at Weitchpec, above the mouth of the larger river on the Pacific Ocean. The confluence marks the point where the Klamath turns from its generally southwesterly course to flow north towards the sea. As the crow flies, Weitchpec is situated about northeast of Eureka.
The Trinity River is a predominantly rain-fed river, with the highest flows occurring between December and April and the lowest from August through October. The water level can rise quickly in the winter when large Pacific storms strike California's north coast. Almost no precipitation occurs in summer, when the primary source of flow is snowmelt from the higher elevations of the Klamath Mountains and groundwater base flow. In addition, diversion of water to the Central Valley has greatly reduced the total flow of the river since the 1960s, though conversely, a required minimum dam release for protection of migrating salmon results in a flow rate during the dry season that is higher than it naturally would be.
Streamflow
The United States Geological Survey (USGS) operates eight real-time stream gages on the Trinity River. The lowermost gage, located at Hoopa, measures runoff from , or 97 percent of the Trinity River watershed. The annual discharge, averaged over the 1964–2013 period, was . The average discharge between 1912 and 1960, prior to construction of Trinity and Lewiston Dams, was . The maximum flow was on December 22, 1964, during the Christmas flood of 1964, and the lowest was on October 4, 1931.
The peak flow in 1964 was greatly attenuated by the Trinity Dam which had just started reservoir filling at the time, perhaps by as much as . However, the record-breaking rains of that winter swelled tributaries below the dam and contributed to a crest fully higher than the second highest peak, recorded in December 1955.
The other USGS gages are located at Coffee Creek (above Trinity Lake), below Lewiston Dam, above and below Douglas City, at Junction City, at Helena, and at Burnt Ranch.
Watershed
The Trinity River's watershed drains a rugged, forested region of California's North Coast. The highest point in the watershed is Sawtooth Peak in the Trinity Alps; the elevation is where the Trinity meets the Klamath River in the town of Salyer. The watershed is almost entirely covered by mountains, with the only level land in a few narrow valleys: the Weaverville basin, and the Hoopa, Hyampom and Hayfork Valleys. The Hayfork Valley is the largest agricultural area in Trinity County, with about of farmland. About 80 percent of the Trinity River watershed is federal land managed by the U.S. Forest Service and the U.S. Bureau of Land Management. The remaining 20 percent are privately owned; about half are owned by logging companies.
The overall climate is Mediterranean, with cool, wet winters and hot, dry summers. Annual precipitation over the Trinity River watershed averages . Precipitation ranges from in lowlands around Weaverville and Hayfork, to as high as in some mountain ranges close to the coast. The high rainfall combined with the rugged geography results in extremely fast runoff and a high risk of flooding during winter storms. Large volumes of rocks and sediment carried by floods are spread along the rivers forming wide alluvial channels. In general, human activities such as mining and road construction have increased the rate of erosion within the watershed and consequentially the amount of sediment carried into the rivers. Dam building has had the opposite effect, by blocking natural sediment sources to a long section of the Trinity River. Both have had notable impacts on river geomorphology, altering the development of riparian zones and fish habitat.
The Trinity River watershed borders several major California drainage basins; these are the Mad River and Redwood Creek to the west, the Salmon River and Scott River (tributaries of the Klamath River) to the north, and Clear Creek and Cottonwood Creek (both tributaries of the Sacramento River) to the east and south, respectively. Fir, oak, and pine forests cover about 92 percent of the watershed. Chaparral and shrubs account for slightly over 5 percent, and grassland and barren land each cover approximately 1 percent. Riparian zones and wetlands encompass 0.5 percent of the watershed. Less than 2 percent of the watershed is urbanized.
About 86 percent of the Trinity River watershed is in Trinity County. As of the 2010 census, the population of Trinity County was 13,786. With a population density of 4.3 people per square mile (1.7/km2) it is one of the least densely populated counties in California. Only , or about 14 percent of the western part of the basin, is in Humboldt County. The part of the Trinity River watershed in Humboldt County is also sparsely populated, with the exception of the Hoopa Valley Reservation, which was home to 2,930 people as of 2011. Extractive industries such as mining and logging, and to a limited extent farming and ranching, have been the main economic drivers in the Trinity River basin since European settlement in the 1800s. These have declined in part due to increasing environmental regulations. Tourism has been an increasingly important part of the economy especially after the creation of the Trinity Lake reservoir in 1964.
Geology The lands that make up the Trinity River basin today began to take shape over 200 million years ago by the collision of several exotic terranes – or crustal fragments of the Pacific Plate – with the North American Plate, causing uplift of the sea floor under what is now northwestern California. During the Jurassic and Cretaceous periods, tectonic movement along the plate boundary produced a range of mountains much higher than those found in the area today. Over millions of years these mountains were eroded, then reformed again as the next oceanic terrane collided with the continental crust. This repeating cycle of erosion and orogeny created the complex "jumble of different rock types" that characterizes the region today. Rocks commonly found in the Trinity River area include gabbro, chert, granite, diorite, limestone, sandstone, serpentine, schist and marble. Gold-bearing quartz veins are widespread in local metamorphic rock formations; the richness of the area made it among the focal points of the California Gold Rush.
The Klamath Mountains, which make up the eastern part of the watershed are quite young in geologic terms, no more than 2 or 3 million years old. The present shape of the mountains was highly influenced by underground volcanic activity, which created batholiths, domes of igneous rock formed by cooled magma. They raised the elevation of the terrain above and created the widespread granite and diorite formations found in the area today. The higher mountains, including the Trinity Alps – the highest range in northwest California – were also sculpted by glaciation during successive Ice Ages, the last of which ended roughly 10,000 years ago. Glacial erosion produced numerous granite outcroppings, tarns, cirques and knife-edged ridges. Remnants of these glaciers, or "glacierets", are still extant in the higher valleys.