ROCK 1946 AZ MARK (HT2469) - Contra Costa County, CA
Posted by: 
alamofox
N 37° 49.063 W 122° 04.084
10S E 582024 N 4186000
Azimuth Reference Mark for Triangulation Station ROCK
Waymark Code: WM18VNX
Location: California, United States
Date Posted: 10/02/2023
Views: 1
This is the last remaining reference mark for the ROCK horizontal control station. The station was located on the top of Rocky Ridge and is now destroyed with this reference marker the last remaining object. The HT2469 recovery notes for 1962 reported that, "THE AZIMUTH MARK WAS RECOVERED IN GOOD CONDITION BUT IT IS APPARENT THE STATION MARK AND REFERENCE MARKS WERE DESTROYEDIN 195 4 DURING CONSTRUCTION OF A MILITARY INSTALLATION AT THE STATION SITE." The azimuth mark has an arrow that points in the direction of the station location. Topographic maps show a ROCK 2 station in the vicinity of the old station, but no detailed data sheets are available for ROCK 2.
The ROCK data sheet describes the azimuth as "...STAMPED ROCK 1946, IS A STANDARD USC AND GS DISK SET IN BEDROCK PROJECTING 30 INCHES ABOVE THE GROUND. IT IS ON THE CENTER ONE OF THREE SMALL HILLS LYING ABOUT 1/4 MILE WEST SOUTHWEST OF THE STATION property. The mark is located on East Bay Municipal Utility District (EBMUD). A trail permit is required to pass onto EBMUD property. Trail permits are available online at (
visit link)
From the paved road on top of Rocky Ridge, follow the Rocky Ridge Loop trail west about 0.15 mile to where it turns toward the north. Follow the use trail that leads farther west and takes you to the crest of the next small ridge. About 100 feet To the north of you is a lone tree. The marker is near this tree.