The Middle Fork American River is one of three forks that form the American River in Northern California. It drains a large watershed in the high Sierra Nevada west of Lake Tahoe and northeast of Sacramento in Placer and El Dorado Counties, between the watersheds of the North Fork American River and South Fork American River. The Middle Fork joins with the North Fork near Auburn and they continue downstream to Folsom Lake as the North Fork, even though the Middle Fork carries a larger volume of water.
The Middle Fork was one of the richest gold mining areas during the California Gold Rush of the 1850s, and is still recreationally mined today. The river is dammed extensively to produce hydroelectricity and provide domestic water supply. Although long stretches of the Middle Fork have been dewatered by diversions, the portion of the river and canyon in the Auburn State Recreation Area is one of the state's most popular whitewater runs. Professional whitewater rafting companies offer guided trips on the Middle Fork American river from May to October. The Middle Fork canyon also has an extensive system of hiking and riding trails including the Western States Trail, which stretches from Auburn to Lake Tahoe.
Course The Middle Fork begins at an unnamed spring in the Granite Chief Wilderness, above sea level, in eastern Placer County, west of the Palisades Tahoe Ski Resort, and about west of Lake Tahoe. The headwaters are in a rugged granite basin fed by multiple streams including one flowing from Little Needle Lake. The river flows west, turning southwest where it receives Talbot Creek from the right, through the high mountain valley of French Meadows. Several campgrounds and numerous public trails are located along this upper reach of the river. About from its source, it enters French Meadows Reservoir, above sea level, formed by the rockfill L.L. Anderson Dam. Almost the entire flow of the river at this point is diverted for hydroelectric generation, to be returned much farther downstream, with the consequence that the river immediately below the dam is reduced to a trickle except during periods of heavy snowmelt.
Below Anderson Dam the Middle Fork begins to form the boundary between the Tahoe National Forest on the north and the Eldorado National Forest on the south, almost to its confluence with the North Fork. It turns south-southwest, flowing through an extremely steep canyon, descending about in to its confluence with Duncan Creek at above sea level. The Middle Fork's canyons, often exceeding in depth, are bounded by extensive high ridges on either side, with Red Star and Chipmunk Ridges to the north and south of the river, respectively, between French Meadows and Duncan Creek. From there downstream to the El Dorado County line the canyon is bounded by Mosquito Ridge to the north, and Ralston Ridge to the south.
At the confluence with Duncan Creek the Middle Fork begins to turn west, winding through its rugged canyon, and flows through the small Interbay Reservoir where more water is diverted for power generation. It receives Big Mosquito Creek from the right and makes a large bend around the north side of Tanner Point. The Middle Fork continues west towards the western end of Ralston Ridge, north of Balderson Station, where it is joined by its largest tributary, the Rubicon River. The Rubicon is significantly longer than the Middle Fork above their confluence, and its drainage basin is also larger, extending to the Desolation Wilderness and draining a large part of northern El Dorado County. Like the upper Middle Fork, the Rubicon is almost entirely diverted for power generation. The diverted water is returned to the Middle Fork at Ralston Afterbay (Oxbow Reservoir), located directly below the confluence of the Middle Fork and Rubicon River at an elevation of .
A short distance below the dam the Middle Fork is joined by its second largest tributary, the North Fork Middle Fork American River, which drains an extensive area along the Forest Hill Divide, though lower in elevation than the upper Middle Fork or Rubicon Rivers. The North Fork Middle Fork is free-flowing with no significant dams or diversions. Just downstream, the Middle Fork flows through Tunnel Chute, where the river races through a man-made tunnel blasted out during the California Gold Rush, in order to dewater part of the river bed for mining. The Middle Fork delineates the Placer County (north)–El Dorado County line from Oxbow Dam all the way until its confluence with the North Fork.
Near Foresthill the Middle Fork leaves the western boundary of the Tahoe/Eldorado National Forests and enters the Auburn State Recreation Area in the foothills of the Sierra Nevada. Its canyon is wider, less steep, and heavily forested, with depths of from rim to river. It receives numerous smaller creeks and canyons including Volcano Canyon from the north near Foresthill, and Otter Creek and Canyon Creek from the south near Georgetown. Although the river has a lower gradient in the foothills, its most dangerous rapid is located here at Ruck-A-Chucky Falls just north of Greenwood. Below Ruck-A-Chucky the Middle Fork makes an abrupt southward jog before turning west-southwest again, joining the North Fork at "The Confluence" at an elevation of . The Confluence is just east of Auburn, directly upstream of Highway 49 and below the Foresthill Bridge.
Watershed
The Middle Fork American River watershed encompasses , which represents about 33 percent of the total American River drainage basin above Folsom Lake. The Rubicon River is the largest tributary watershed, at , which is nearly three times the size of the Middle Fork's own drainage area above their confluence. Almost the entire watershed is forested, with the exception of the alpine zone at the highest elevations near the Sierra Crest, and some areas of grassland, range and shrub in the foothills.
Elevations range from at the river's mouth to over at the headwaters of the Rubicon River. More than half of the watershed is or more above sea level. The terrain is extremely rugged, with many areas of thin, rocky soils that pose a high erosion hazard. Drainage generally occurs in a southwesterly direction between a series of long parallel ridges. With the Forest Hill Divide forming the northern boundary of the watershed, the major ridges heading south are Deadwood, Mosquito, Red Star, Ralston/Chipmunk and Nevada Point Ridges. The sole exception to this drainage pattern is the headwaters of the Rubicon River, which flow in a northwesterly direction before turning southwest.
The watershed is sparsely populated. The largest communities are Georgetown and Foresthill, which respectively had populations of 2,367 and 1,483 as of the 2010 census. There is also a number of smaller unincorporated communities including Todd Valley, Michigan Bluff, and Volcanoville, all of which began life as mining camps during the Gold Rush. The largest nearby city is Auburn, which with about 13,000 people is one of the northeasternmost communities in the Sacramento metropolitan area. About 75 percent of the watershed is managed by the U.S. Forest Service, with the balance split between the U.S. Bureau of Land Management, the state of California, and private landowners. In the lower part of the watershed, below the confluence with the Rubicon River, about half of the land is privately owned, with rural residential and some logging as the major uses.
The Middle Fork is one of the highest precipitation watersheds on the western slope of the Sierra Nevada, with an annual average of with a range of from the foothills to the mountains. Since the area experiences a Mediterranean climate, most of the precipitation occurs between November and March. At elevations higher than , most precipitation falls as snow; elevations higher than are often covered in snow until late May or early June. Flows in the upper Middle Fork and Rubicon Rivers are dominated by snowmelt; the North Fork Middle Fork is equally affected by snowmelt and rainfall, and tributaries of the lower Middle Fork depend mostly on rainfall.
Water flow in the Middle Fork has been extensively modified by dams and diversions, with late spring-early summer high flows stored in reservoirs to generate hydropower later in the year when natural runoff is at its lowest. The impact on the annual hydrograph is shown in the below charts (French Meadows and Hell Hole reservoirs were created in 1964 and 1996, respectively):
Middle Fork monthly mean discharge at Auburn, 1911–1966 (cfs)
Middle Fork monthly mean discharge at Auburn, 1966–1986 (cfs)
Ecology The Middle Fork watershed contains numerous distinct plant communities. A study conducted by the Middle Fork of the American River Restoration Project (2011) identified five forest types in the upper Middle Fork and the North Fork Middle Fork watersheds. Mixed conifer forests, consisting mainly of ponderosa pine, sugar pine, Jeffrey pine, incense-cedar, white fir, Douglas fir, black oak and interior live oak, encompass 51 percent of this area, mostly at elevations below . Some of this area is considered hardwood-conifer forests, which are dominated by oaks with more dispersed stands of conifers. White fir forests are the second largest group, comprising about 22 percent of the total area. Red fir forests, encompassing about 13 percent of the total, are found mostly at higher elevations. At lower elevations, hardwood forests cover about 11 percent of the watershed, mostly on hillsides and in canyons. Certain south-facing slopes at lower elevations are dominated by chaparral and to a lesser extent, grasslands. The Placer County Grove, located just northwest of the Middle Fork/Duncan Creek confluence, is the northernmost and most isolated grove of giant sequoias in California. It contains six trees, believed to range from 1,000 to 2,000 years old; the Joffre Tree is the tallest, standing high.
Due to fire suppression since the beginning of the 20th century, white fir has become more prevalent in the mixed-conifer forests while some pines, especially yellow pine and sugar pine, have declined significantly. Fuel loading in forests has increased due to interruption of the natural fire cycle, leading to an increase in the number and intensity of fires in recent decades. Plant communities in the Middle Fork have also been impacted by grazing, mining, road construction, selection cutting of larger trees, and other human activities.
Riparian habitat along the Middle Fork is limited due to the rocky substrate, heavy sedimentation, and frequent flooding that scours the river channel; however, many smaller tributaries host healthy riparian zones. Except for the headwaters, the Middle Fork is generally a wide, gravel-bedded stream with a pool and riffle morphology. Water quality in the Middle Fork is considered fair to good, but fish spawning habitat has been reduced by the construction of dams and water diversion for hydropower.
The Middle Fork is home to many fish species; rainbow trout, brown trout, Sacramento sucker, and Sacramento pikeminnow are found along the length of the river, and smallmouth bass are present in most of the major reservoirs and lakes. Fish found only in the lower elevations of the river include hardhead, riffle sculpin, and prickly sculpin. At higher elevations, brook trout are found; cutthroat trout, lake trout and kokanee salmon also live at higher elevations but have only been reported in Hell Hole Reservoir and the Rubicon River upstream of there.
Various other wildlife species are found along the Middle Fork including deer, black bears, mountain lions, bobcats, river otters, golden eagles, and bald eagles. More than 20 endangered, threatened or sensitive wildlife species have been found in the watershed, including the Sierra Nevada yellow-legged frog, California red-legged frog and California spotted owl.
Human history