Longitude: 119°23.740' W
I found this mark along the Sierra Scenic Byway. It was indentified as a U.S.Bureau of Public Roads mark, stamped with a date of "1952". Additional stamping included a project station of "636+01.52", a benchmark elevation of "4597.35", and "21.13", possibly a mile mark.
I had never seen a mark placed by the U.S.Bureau of Public Roads, let alone heard of them. A quick internet search found the following:
The Federal Highway Administration (FHWA) was created on October 15, 1966, however it has several predecessor organizations and a complicated history. The first predecessor was the Office of Road Inquiry (ORI) founded on in 1893. In 1905 that organization's name was changed to the Office of Public Roads (OPR), and it became a division of the United States Department of Agriculture. The name was changed to Bureau of Public Roads (BPR) in 1915. In 1939 the name was changed to Public Roads Administration (PRA) and it was shifted to the Federal Works Agency (FWA). With the abolition of the FWA in 1949, its name was changed back to BPR and it was shifted to the Department of Commerce. In 1967 the BPR was transferred to the newly created FHWA, and was one of three original bureaus along with the Bureau of Motor Carrier Safety and the National Highway Safety Bureau (now known as NHTSA).