The 1st District stretches along the eastern edge of the state, from the Oregon border to the Mojave Desert. It includes most of the Mother Lode and Sierra Nevada Regions in addition to Lake Tahoe. However, because most of the district is rural, two-thirds of the district's population in 2000 lived in suburban Sacramento.
It includes the entirety of Modoc, Lassen, Plumas, Sierra, Amador, El Dorado, Calaveras, Alpine, and Mono Counties. It also contains parts of Nevada County (including Truckee), Placer County (including Auburn, Colfax, and Roseville), and Sacramento County (including all of Fair Oaks, Folsom, Galt, Gold River, Orangevale, Rancho Murrieta, Vineyard, and Wilton; and most of Carmichael, Elk Grove and Rancho Cordova).