Modoc County

According to the U.S. Census Bureau, the county has a total area of 4,203 square miles (10,890 km2), of which 3,918 square miles (10,150 km2) is land and 286 square miles (740 km2) (6.8%) is water.

There are 2.25 persons per square mile, making this one of the most sparsely populated counties in California. It is also (almost) the only rectangular county in California, there is a slight deviation around the Tule Lake National Wildlife Refuge.

The county is very diverse geographically. The northwestern edge of the county is dominated by the Medicine Lake Highlands, the largest shield volcano on the U.S. West Coast. The Lava Beds National Monument lies partly within the northwest corner of the County. Also along the western edge of the county is the massive Glass Mountain lava flow. The southwestern corner of the county is a unique ecosystem of isolated hardwoods (oaks) and volcanic mountains with intermountain river valleys.

The northern half of the county is the Modoc Plateau, a 1-mile (1.6 km) high expanse of lava flows, cinder cones, juniper flats, pine forests, and seasonal lakes, plus the alkaline Goose Lake. Nearly 1 million acres (4,000 km²) of the Modoc National Forest lie on the plateau between the Medicine Lake Highlands in the west and the Warner Mountains in the east. The plateau supports large herds of mule deer (Odocoileus hemionus), Rocky Mountain Elk (Cervus canadensis), and pronghorn (Antilocapra americana). There are also several herds of wild horses on the plateau. The Clear Lake National Wildlife Refuge and Long Bell State Game Refuge are located on the plateau as well. The Lost River watershed, which later drains into the Klamath River basin, drains the north part of the plateau, while southern watersheds either collect in basin reservoirs or flow into the large Big Sage Reservoir, which sits in the center of the county, which later flows into the Pit River.

Below the rim of the Plateau is Big Valley in the extreme southwest corner of the county, and the large Warm Springs Valley that forms the bottom of the Pit River watershed that runs through the county. The north fork and south fork of the Pit River come together just south of Alturas. The River collects hundreds of other small creeks as it flows south towards Lake Shasta, where it joins the Sacramento River and drains into the San Francisco Bay.

The eastern edge of the county is dominated by the Warner Mountains. The Pit River originates in this mountain range. Hundreds of alpine lakes dot the range, all of which are fed by snow-melt and natural springs. East of the Warner Range is Surprise Valley and the western edge of the Great Basin.

Hot Springs and lava caves are common to Modoc County. There are some geothermal energy resources available in the county, though their viability is highly variable.

A great diversity of plants are found in Modoc County, since this is situated within the biodiverse California Floristic Province. Numerous native trees are found in the county including Garry Oak and Washoe Pine trees.[11] Jeffrey Pine and Ponderosa Pine are also found in large numbers.