Chris: With great input from Earl I think the MP in the photo is 311 prior to the La Veta route realignment. Here's what Earl emailed me:
"When the standard gauge was built over La Veta Pass in 1899, the new route was 1.4 miles longer, so all the mile posts west of Wagon Creek Jct where the new standard gauge line re-connected with the existing old grade to Alamosa were moved 1.4 miles east.
Alamosa was mile post 250.3 on the narrow gauge route, 251.7 on the standard gauge route"
Currently MP 311 is about 1.4 miles east of where it appears in the photo. It's now in the vicinity of the west switch of Toltec Siding.
Rich