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.

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.