I've been to the geographic center of California:
The geographic center of the state of California is located between North Fork and Italian Bar. The point is about 7.1 miles driving distance from the United States Forest Service office in North Fork.
The location is marked by a sign and a survey marker. NAD83 coordinates for the exact center of California are 37°09′58″N, 119°26′58″W The Fresno County line is less than one mile, (straight-line distance), from the site's survey marker. The site is also marked on the United States Forest Service road map of Sierra National Forest, which can be purchased at the North Fork USFS office. The actual site has wooden stairs leading up the hillside about 50 feet from the road. The marker is not wheelchair accessible.
Italian Bar Rd., the road to the geographic center marker, is paved with a smooth surface and is usable by ordinary passenger cars. The road is narrow and meeting a large truck, such as Forest Service fire rig, may require maneuvering to allow passage. A local resident of Italian Bar Road with a sense of humor has posted a sign in their front yard: GEOGRAPHIC CENTER PARKWY.
It's on someone's property but the marker is not far from the small road. When I was there years ago, it was marked by a wooden stake with a yellow ribbon.