Our Ecology

Originally authored by Richard Hanes and Chet Blackburn

Nevada and Placer Counties are located in Northern California, northeast of Sacramento, in the northern Sierra Nevada. Their western edges lie in the valley grasslands and lower foothills along the eastern side of the Sacramento Valley. The counties then extend eastward, over the crest of the Sierra to the Nevada state line, which forms the eastern boundary.

Much of the northern boundary of Nevada County is formed by the Middle Yuba River, and the southern boundary of Placer County the Middle Fork of the American River and the Rubicon River.

Boundaries, Sizes, and Populations of Our Counties

The smaller and more northern of the two counties is Nevada County, an area occupying 974 square miles.The shape of the county resembles that of the small pistol known as the Derringer, a popular icon of the fictional old West.

The population of Nevada County in 2000 was slightly more than 92,000 people, 99,000 as of 2017. Placer County lies south of Nevada County and covers an area of 1,504 square miles.The population of Placer County in 2000 was just under 250,000, most of which was concentrated in the populous western edge of the county in the cities of Roseville and Rocklin, to which continuous subdivisions from Sacramento now extend. As of 2017, there were 386,000 people in Placer County. The western edge of Placer County is one of the fastest-growing areas in the state.

Geology, Elevations, and Water

The Sierra Nevada is the dominant feature of the area, but the two counties are much more diverse than that situation might imply. Elevations range from under 40 feet in Placer County at the juncture where the Placer, Sacramento, and Sutter County boundaries converge, to 9,143 feet at Mt. Lola in Nevada County and 9,006 feet at Granite Chief in Placer County.

The Sierra Nevada began forming approximately 210 million years ago when molten magma beneath what was then a shallow sea floor began to slowly cool to form a huge granite batholith. In the process, it began lifting the sedimentary rock forming the sea floor. The old rock layers were lifted as a block and tilted upward, resembling a partially open trap door with the western slope gradually ascending eastward to the summit, then dropping sharply on the eastern side.

Although the gradient of the eastern slope is steep, it is not as steep as it is in most parts of the southern Sierra, because in our area the descent is into the high Tahoe and Truckee basins that lie between the Sierra and the Carson Range in Nevada. The elevation at the surface of Lake Tahoe is 6,225 feet, while that of Truckee is just under 6,000 feet.

The western slope is heavily dissected by numerous fast-flowing streams that have carved narrow ridges and deep canyons into the older rock formations. This process has resulted in the formation of some of the most rugged country to be found anywhere in the state. The largest watercourses are the North and Middle Forks of the American River, the Rubicon River, the Bear River, and the Yuba River, but numerous other permanent and intermittent streams under 6,000 feet feed into them.

The headwaters of the major drainages, most of which are fed by melting snow, start in the glaciated crest zone. The headwaters for the South Yuba River, the North and Middle Forks of the American River, the Bear River, Rubicon River, and Truckee River all start in our area. The Middle Yuba River headwaters are just to the north in Sierra County.

There are numerous natural and man-made lakes in this part of the Sierra. Our area includes a portion of Lake Tahoe, as well as Donner Lake, Fordyce Lake, French Lake, and many smaller lakes created by both glaciations and human beings. Some of the major reservoirs are Boca, Prosser, Independence, French Meadows, Bowman, Spaulding, Ralston, Rollins, and a portion of Folsom Lake.

Much of the land in our counties is within the Tahoe and El Dorado National Forests, although there are many parcels in private ownership that form a checkerboard pattern throughout the national forest lands.

All three of the major categories of rock (igneous, sedimentary, and metamorphic) are found within the two counties and each is found in abundance, including but not limited to such different kinds of rock as granite, andesite, diorite, sandstone, shale, limestone, slate, green-stone, various schists, serpentine, gabbro, and others. The geology is so diverse and complex that in some areas, such as the American River Canyon outside of Auburn, all three major types occur within short distances of each other.

As would be expected, the various soils derived from the weathering of the many different types of rock are themselves unique.

The serpentine and gabbro soils in particular represent a special situation. They are high in heavy metal content such as chromium and nickel and deficient in the calcium, nitrogen, and phosphorus required for plant growth; hence they tend to be toxic or hostile to the growth of many plant species. As a result they have developed a unique flora capable of withstanding those conditions better than other plants.

An example of the sharp climatic differences due to elevation can be seen in the contrast between Rocklin and Blue Canyon, only 50 miles to the east. Rocklin, at an elevation of 250 feet, averages 75 days a year above 90°F and 16 days below freezing, while Blue Canyon. at 5,300 feet, averages less than 1 day a year above 90°F and 96 days below freezing.

Rich Flora Diversity

Such incredible diversity in elevation, topography, climate, geology, and soils is responsible for the rich flora to be found here. Of the 5,862 species of native plants listed in the 1993 edition of The Jepson Manual: Higher Plants of California, more than 2,000 of them are locally native to our two-county area. Although the combined area of Nevada and Placer Counties occupies only 1.5 percent of California’s 163,707 square miles, 38 percent of the plant species that are found within California can be found growing here.