USDI/NPS Monument No. 310 - Gettysburg, PA
N 39° 48.291 W 077° 13.346
18S E 309746 N 4408460
A small, tiny, once bronze disk (now green) is set into the top of a concrete rectangular prism acts a a boundary marker for the Gettysburg National Military Park Historic District.
Waymark Code: WMH766
Location: Pennsylvania, United States
Date Posted: 06/02/2013
Views: 11
There is a sizable collection of these benchmarks about the park. I have found 8 and Ernmark has found 2. There is certainly more but they are unfound and given their age and condition I doubt there is an official list and location file available to know how many there are of these markers for sure. The marker rests in a concrete prism-shaped monument, less than a foot high and is located to the immediate right of the 
Batteries B & L, 2nd U.S. Artillery Monument. There is also a U.S. Boundary Monument directly to the right of this, a few inches away, also small, made of granite but just lower to the ground.
This marker is located on the right or south side of Granite Schoolhouse Lane if traveling west. If traveling south along Taneytown Road, you would turn left or east onto Granite Schoolhouse Lane to get to this monument which is .4 of mile down the road. Parking is available roadside but it is not the best place to pull over as the road is narrow so exercise caution. Do not park on the grass or you will be ticketed by Park Police. I visited this monument on Monday, August 13, 2012 at 12:28 PM, EDT, just before the clocks were set ahead for the Spring. I was at a 537 foot ASL elevation.
The monument is in pretty good condition. It was probably installed when this battlefield gained official historic district status although the greening of the disc may indicate a much older benchmark. The marker simply reads USDI - NPS 310. These latters stand for U.S. Department of Interior - National Park Service. I suppose the number 310 is some kind of internal inventory system for keeping track of these things. This is similar to the other markers I found. One of the monuments in this series actually has a numerical-letter designation so I do not know what the thinking was when these were surveyed and installed. There are slight variations in some of these things.