Eastern California is not a well-defined term. It generally refers to the strip of California to the east of the crest of the Sierra Nevada, or to the easternmost counties of California:

• Modoc County
• Lassen County
• Plumas County
• Sierra County
• Nevada County
• Placer County
• El Dorado County
• Alpine County
• Mono County
• Inyo County
• San Bernadino County
• Riverside County
• Imperial County

Eastern California does not fit the stereotypes of California. Because it is generally in the rain shadow of the Sierra Nevada or the Transverse Ranges, the climate is extremely dry and can be considered a desert. Indeed, the hottest and lowest area in North America lies in Eastern California: Death Valley.

Eastern California is also very sparsely populated (except for the area around Lake Tahoe), and tends to be politically conservative, much like the rest of the rural Western United States.

Geologically, Eastern California is mostly part of the Basin and Range Province, marked by crustal extension, with horsts and grabens. Volcanism is also very evident in this region.