Alpine County is a county in the eastern part of the U.S. state of California located within the Sierra Nevada on the state border with Nevada. As of the 2020 Census, the population was 1,204, making it California's least populous county. The county seat and  largest community is Markleeville.From ski resorts to the back country, kayaking and fishing, Alpine County is a World-Class adventure destination.

Amador County is a county located in the U.S. state of California, in the Sierra Nevada. As of the 2020 census, the population was 40,474. The county seat is Jackson. Amador County, located within California's Gold Country, is known as "The Heart of the Mother Lode". There is a substantial viticultural industry in the county.

Butte County, "The Land of Natural Wealth and Beauty”, is a county located in the northern part of the U.S. state of California. In the 2020 census, its population was 211,632. The county seat is Oroville.

Butte County comprises the Chico, CA metropolitan statistical area. It is in the California Central Valley, north of the state capital of Sacramento.

Butte County is drained by the Feather River and the Sacramento River. Butte Creek and Big Chico Creek are additional perennial streams, both tributary to the Sacramento. The county is home to California State University, Chico and Butte College.

Calaveras County, officially the County of Calaveras, is a county in both the Gold Country and High Sierra regions of the U.S. state of California. As of the 2010 census, the population was 45,292. The county seat is San Andreas. Angels Camp is the county's only incorporated city. Calaveras is Spanish for "skulls"; the county was reportedly named for the remains of Native Americans discovered by the Spanish explorer Captain Gabriel Moraga. Calaveras Big Trees State Park, a preserve of giant sequoia trees, is in the county several miles east of the town of Arnold on State Highway 4 and the county is Home of the Jumping Frog Jubilee.

Colusa County is a county located in the U.S. state of California. As of the 2020 census, the population was 21,839. The county seat is Colusa. It is in the North Valley of California, northwest of the state capital, Sacramento. A large number of streams drain the county, including Elk Creek, Salt Creek, Stony Creek and Bear Creek.

The county's eastern boundary is formed, in part, by the Sacramento River.

El Dorado County officially the County of El Dorado, is a county located in the U.S. state of California. As of the 2020 census, the population was 191,185.^[ El Dorado County, located in east-central California, encompasses 1,805 square miles of rolling hills and mountainous terrain. The County’s western boundary contains part of Folsom Lake, and the eastern boundary is also the California-Nevada State line. The County is topographically divided into two zones. The northeast corner of the County is in the Lake Tahoe basin, while the remainder of the County is in the “western slope,” the area west of Echo Summit. This landscape invites residents and tourists alike to enjoy outdoor recreation activities year-round.There are two municipalities within El Dorado County. The largest city in the County is the City of South Lake Tahoe, with a 2019 population of 22,197. The City of Placerville, the County seat, is located 45 miles northeast of Sacramento, the State capital. The City of Placerville has a 2019 population of 10,970. The remainder of the County’s approximate 156,000 residents lives outside of the two incorporated areas.

Glenn County is a county located in the U.S. state of California. As of the 2020 census, the population was 28,917.The county seat is Willows.It is located in the Sacramento Valley, in the northern part of the California Central Valley. The Grindstone Rancheria, reservation of the Grindstone Indian Rancheria of Wintun-Wailaki Indians, is located in Glenn County. 

Inyo County is a county in the eastern central part of the U.S. state of California, located between the Sierra Nevada and the state of Nevada. In the 2020 census, the population was 19,016. The county seat is Independence. Inyo County is on the east side of the Sierra Nevada and southeast of Yosemite National Park in Central California. It contains the Owens River Valley; it is flanked to the west by the Sierra Nevada and to the east by the White Mountains and the Inyo Mountains. With an area of 10,192 square miles (26,397 km), Inyo is the second-largest county by area in California, after San Bernardino County. Almost one-half of that area is within Death Valley National Park. However, with a population density of 1.8 people per square mile, it also has the second-lowest population density in California, after Alpine County. 

Lassen County is a county in the northeastern portion of the U.S. state of California. As of the 2020 census, the population was 32,730. The county seat and only incorporated city is Susanville. Lassen County comprises the Susanville, California, micropolitan statistical area. A former farming, mining and lumber area, its economy now depends on employment at one federal and two state prisons; the former in Herlong and the latter two in Susanville. In 2007, half the adults in Susanville worked in one of the facilities.

Madera County officially the County of Madera, is a county at the geographic center of the U.S. state of California.[2] As of the 2020 census, the population was 156,255.[3] The county seat is Madera.[4] Madera County comprises the Madera, CA Metropolitan Statistical Area, which is included in the Fresno-Madera, CA Combined Statistical Area. It is located in the eastern San Joaquin Valley and the central Sierra Nevada. The southeasternmost part of Yosemite National Park is located in the county's northeast. 

Mariposa County is a county located in the U.S. state of California. As of the 2020 U.S. Census, the population was 17,131.  The county seat is Mariposa.  It is located in the western foothills of the Sierra Nevada mountains, north of Fresno, east of Merced, and southeast of Stockton.

The county's eastern section is the central portion of Yosemite National Park.

There are no incorporated cities in Mariposa County; however, there are communities recognized as census-designated places for statistical purposes. It also has the distinction of having no actual traffic signals anywhere in the county. (The only other counties in California with no incorporated cities are Alpine and Trinity.)

Modoc County is a county in the far northeast corner of the U.S. state of California. Its population is 8,700 as of the 2020 census, down from 9,686 from the 2010 census. This makes it California's third-least populous county. The county seat and only incorporated city is Alturas.Previous county seats include Lake City and Centerville. The county borders Nevada and Oregon.

Much of Modoc County is federal land. Several federal agencies, including the United States Forest Service, Bureau of Land Management, National Park Service, Bureau of Indian Affairs, and the United States Fish and Wildlife Service, have employees assigned to the area, and their operations are a significant part of its economy and services.

The county's official slogans include "The last best place" and "Where the West still lives”.

Mono County is a county located in the east central portion of the U.S. state of California. As of the 2020 census, the population was 13,195, making it the fourth-least populous county in California. The county seat is Bridgeport. The county is located east of the Sierra Nevada between Yosemite National Park and Nevada. The only incorporated town in the county is Mammoth Lakes, which is located at the foot of Mammoth Mountain. Other locations, such as June Lake, are also famous as skiing and fishing resorts. Located in the middle of the county is Mono Lake, a vital habitat for millions of migratory and nesting birds. The lake is located in a wild natural setting, with pinnacles of tufa arising out of the salty and alkaline lake. Also located in Mono County is Bodie, the official state gold rush ghost town, which is now a California State Historic Park.

Nevada County is a county located in the U.S. state of California, in the Sierra Nevada. As of the 2020 census, its population was 102,241. The county seat is Nevada City. Nevada County comprises the Truckee-Grass Valley micropolitan statistical area, which is also included in the Sacramento-Roseville combined statistical area, part of the Mother Lode Country. According to the U.S. Census Bureau, the county has a total area of 974 square miles (2,520 km), of 16 square miles (41 km) (1.6%) are covered by water. The county is drained by  Middle and South Yuba Rivers.Nevada County is home to the Empire Mine State Historic Park, which is the site of one of the oldest, deepest, and richest gold mines in California. The park is in Grass Valley at 10791 East Empire Street. In operation for more than 100 years, the mine extracted 5.8 million ounces of gold before it closed in 1956.

Placer County; (Spanish for "sand deposit"), officially the County of Placer, is a county in the U.S. state of California. As of the 2020 census, the population was 404,739. The county seat is Auburn.

Placer County is included in the Greater Sacramento metropolitan area. It is in both the Sacramento Valley and Sierra Nevada regions, in what is known as the Gold Country. The county stretches roughly 65 miles (105 km) from Sacramento's suburbs at Roseville to the Nevada border and the shore of Lake Tahoe.

According to the U.S. Census Bureau, the county has an area of 1,502 square miles (3,890 km), of which 1,407 square miles (3,640 km) is land and 95 square miles (250 km) (6.4%) is water. Watercourses in Placer County include the American River and Bunch Creek. 40.96% of Lake Tahoe's surface area is in Placer County, more than in any of the four other counties in which it lies

Plumas County is a county in the Sierra Nevada of the U.S. state of California. As of the 2020 census, the population was 19,790.The county seat is Quincy, and the only incorporated city is Portola. The largest community in the county is East Quincy. The county was named for the Spanish Río de las Plumas (the Feather River), which flows through it. The county itself is also the namesake of a native moth species, Hadena plumasata.

Plumas National Forest's 1,200,000 acres (4,900 km) offer a wide variety of outdoor recreation opportunities, including hiking, camping, kayaking, swimming, mountain biking, hunting and fishing. The area has more than 100 natural and artificial lakes. Many of the natural lakes are glacial in origin and can be found in and around Lakes Basin Recreation Area.The artificial lakes include Lake Almanor, Lake Davis, Frenchman Lake, Little Grass Valley Reservoir, Antelope Lake, and Bucks Lake. Plumas County also has more than 1,000 miles (1,600 km) of rivers and streams. All three forks of the Feather River run through the area.

Shasta County officially the County of Shasta, is a county in the northern portion of the U.S. state of California. Its population is 182,155 as of the 2020 census, up from 177,223 from the 2010 census. The county seat is Redding.

Shasta County comprises the Redding, California metropolitan statistical area. The county occupies the northern reaches of the Sacramento Valley, with portions extending into the southern reaches of the Cascade Range.

Points of interest in Shasta County include Shasta Lake, Lassen Peak, and the Sundial Bridge.

Sierra County is a county located in the U.S. state of California. As of the 2020 census, the population was 3,236,making it California's second-least populous county. The county seat is Downieville;the sole incorporated city is Loyalton. The county is in the Sierra Nevada, northeast of Sacramento on the border with Nevada. The county is known for its natural beauty and rich history, providing a diverse range of landscapes, from rugged mountains to lush forests, tranquil lakes, and streams, and much more. The area is a great place for outdoor enthusiasts, with opportunities for hiking, fishing, hunting, and exploring the natural wonders of the Sierra Nevada.

Siskiyou County is a county located in the northernmost part of the U.S. state of California. As of the 2020 census, the population was 44,076. Its county seat is Yreka and its highest point is Mount Shasta.It falls within the Cascadia bioregion.

Siskiyou County is in the Shasta Cascade region along with the Oregon border. Because of its outdoor recreation, Mt. Shasta, McCloud River, and Gold Rush era history, it is an important tourist destination within the state.

Sutter County is a county located in the U.S. state of California. As of the 2020 census, the population was 99,633. The county seat is Yuba City. Sutter County is included in the Yuba City, CA Metropolitan Statistical Area as well as the Sacramento-Roseville, CA Combined Statistical Area. The county is located along the Sacramento River in the Sacramento Valley.

According to the U.S. Census Bureau, the county has a total area of 608 square miles (1,570 km), of which 602 square miles (1,560 km) is land and 6.1 square miles (16 km), comprising 1.0%, is water. It is the fourth-smallest county in California by total area. Some 88 percent of the county is prime farmland and grazing land.

Sutter County is home to the Sutter Buttes, known as the "World's Smallest Mountain Range." This volcanic formation provides relief to the otherwise seemingly flat Sacramento Valley.

Bordered by the Sacramento River on the west and the Feather River on the east, Sutter County has 240 miles (390 km) of levees. The Sutter Bypass, which diverts flood waters from the Sacramento River, cuts through the heart of Sutter County. 

Tehama County (Wintun for "high water") is a county located in the northern part of the U.S. state of California. As of the 2020 census, the population was 65,829.The county seat and largest city is Red Bluff.

Tehama County comprises the Red Bluff, California micropolitan statistical area, which is also included in the Redding-Red Bluff, California combined statistical area. The county is bisected by the Sacramento River.

Tuolumne County officially the County of Tuolumne, is a county located in the U.S. state of California. As of the 2020 census, the population was 55,620. The county seat and only incorporated city is Sonora.

Tuolumne County comprises the Sonora, CA Micropolitan Statistical Area. The county is in the Sierra Nevada region.

A California Department of Forestry document reports Tuolumne County's 1,030,812 acres (4,171.55 km) include federal lands such as Yosemite National Park, Stanislaus National Forest, Bureau of Land Management lands, and Indian reservations. Notable landforms in the county include Table Mountain.

Yuba County is a county in the U.S. state of California. As of the 2020 U.S. Census, its population was 81,575.The county seat is Marysville. Yuba County is included in the Yuba Citymetropolitan statistical area, which is also included in the Sacramento–Roseville combined statistical area. The county is in the Central Valley region along the Feather River.

Despite its name and proximity, Yuba City is in neighboring Sutter County, not Yuba County.

It is California's fifth-smallest county by area. The county lies along the western slope of the Sierra Nevada, the steep slopes making it prime territory for the siting of hydroelectric power plants.