US Coast & Geodetic Survey
US COAST & GEODETIC SURVEY REFERENCE MARK
FOR INFORMATION WRITE TO THE DIRECTOR, WASHINGTON DC
$250 FINE OR IMPRISONMENT FOR DISTURBING THIS MARK
and in the centre of the disc, an arrow pointing approximately west with markings stamped on either side. Above:
I'm curious: what is this? In 1946 you may have had to write to the Director of the Coast & Geodetic Survey to find out. But in 2005 we have the Web to hand.
The US Coast & Geodetic Survey is now (and since 1970) the National Geodetic Survey, part of the National Ocean Service (NOS), which in turn is part of the National Oceanographic & Atmospheric Administration (NOAA). The NOAA's fluff page for the NGS has a photo of a marker disc very much like the one I found.
The main NGS webpage is very dry; surveying's a serious business, you know. But it turns out that you can look up marker positions online by doing a datasheet search. Annoyingly, you can't link to datasheet search results; but to find mine, retrieve a DATASHEET by station name NUECES in CALIFORNIA.
But wait: I found a sneaky back route to get a datasheet link. If you search using the NOS's Data Explorer; set a topic of Geodetic Control Point; zoom the map down further and further until you find the green dot corresponding to your marker; and then click "Link To Data" and click on your green dot; and then show the Address Bar in the page it pops up... you end up with a datasheet URL something like... this.
It would seem that what I found was Reference Mark 1 for the Nueces survey station; in addition to the mark I found, there should be discs for the station itself (7.2 metres west of Reference Mark 1; hence the westward arrow on Mark 1) and for Reference Mark 2 (7.5 metres west of the station) plus an additional Azimuth Mark disc set into a concrete post 0.5 miles northwest.
The 1946 directions to the station predate by a long way the establishment of Walnut Creek Open Space in 1974, and refer to roads and landmarks which no longer exist. Ygnacio Avenue is now Ygnacio Valley Road; the Mt. Diablo Road is Walnut Avenue. Las Lomas Way does still exist and does lead down to the Open Space, although it's not a trailhead.
The station was last "recovered" — the markers located and verified OK — in 1955 by both EBMUD and the Coast & Geodetic Survey. You can enter recovery information online; if I ever find all 4 markers for the station I might give it a go...
It would seem that there are (or at least were) six markers in downtown Walnut Creek:
HT0104 (X 178): Mount Diablo & Granger, reported not found 1997
HT0105 (WGB EBMUD): Mount Diablo & California, reported good 1958
HT0106 (WGBI EBMUD): Mount Diablo & Locust, reported not found 1997
HT0107 142.29 C OF WC): North Broadway & Walker, reported not found 1987
HT0108 (134.19 C OF WC): North Broadway & Cypress, reported good 1958
HT0109 (2 C OF WC): Lincoln Avenue & Live Oak Way, reported good 1997
I'll keep my eyes open and see if I can spot any of them.