There are several county routes in Lake County, California

Lake County, California

Lake County is a county located in the north central portion of the U.S. state of California, north of the San Francisco Bay Area. It takes its name from Clear Lake, the dominant geographic feature in the county and the largest natural lake wholly within California...

 that are numbered using a different system than that of the rest of the state. County routes in California

County routes in California

In the U.S. state of California, county routes are controlled and maintained by the respective counties in which they reside. However, they are generally patrolled by the state's California Highway Patrol....

 are typically numbered using a region letter followed by a number. Routes in Northern California

Northern California

Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...

 are in regions A, B and D. Central California

Central California

Central California, sometimes referenced as Mid-State, is an area of California south of the San Francisco Bay Area and north of Southern California...

 has regions E, G and J while letters N, R and S are assigned to Southern California

Southern California

Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

. Lake County uses numerical designations for their county routes, bypassing the alphanumeric designations of the rest of the state.

County Route 145

County Route 145 is a county highway in Lake County. It was paved in 1984.

County Route 502

County Route 502 is a county highway in Lake County. It was constructed to allow access to Konocti Bay.

County Route 505

County Route 505, also known as Gaddy Lane, is a county highway in Lake County.

County Route 515

County Route 515 is a county highway in Lake County. It serves The Geysers

The Geysers

The Geysers is a complex of 22 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains north of San Francisco, California.The largest in the world, the Geysers has...

, as well as residents on Cobb Mountain

Cobb Mountain

Cobb Mountain is the tallest mountain in the Mayacamas Mountains of California. Its 4720+ feet, main summit is located in Lake County, west of the town of Cobb...

.