Madera County Road 400 is an approximately twenty-four-mile roadway following the course of the Fresno River in the Sierra Nevada Mountains. Road 400 begins at California State Route 145 near Madera and terminates to the north at Road 415 near Coarsegold. Traditionally Road 400 was known as "River Road" prior to Madera County dropping naming conventions on county highways. Road 400 was part of the original Yosemite Stage Route by the Washburn Brothers which began in 1882. The Yosemite Stage Route would be realigned to the west in 1886 along what is now Road 600 to a rail terminus in Raymond. Parts of Road 400 were realigned in 1974 to make way for the Hensley Lake Reservoir.
https://www.gribblenation.org/2024/04/madera-county-road-400-and-1882-1886.html?m=1