- District 10 is one of the most geographically diverse districts within the California Department of Transportation. Founded in 1924, District 10 lies in the northern San Joaquin Valley and headquartered in Stockton. The district encompasses three urban counties on the valley floor and five rural counties located in the foothill and mountain region of the Central Sierra, including two mountain counties bordering Yosemite National Park. These eight counties include Alpine, Amador, Calaveras, Mariposa, Merced, San Joaquin, Stanislaus and Tuolumne. The district is responsible for 3,670 miles of State Routes, which includes four Sierra passes, three rest areas, 29 cities, the Port of Stockton and numerous transit authorities. The major urban areas in the district are the cities of Stockton, Modesto and Merced, with a combined population of approximately 1.5 million. The district borders the East Bay Area and continues to experience increased levels of congestion due to heavy commuter traffic through the Altamont Pass and other routes connecting to the Bay area. In addition, the five mountain counties continue to experience growth, while the agriculture communities flourish and development is primarily focused next to existing foothill communities.