Lovely memory, Eleanor. Let's see, I have driven through most of the towns in the San Luis Valley (except Center), and the ones that impress me as being the most tree filled are those towns along Hwy. 160 (runs west-east), as Dave said Monte Vista is, and also Saguache, located way up at the NW corner of the valley. Highway 17 has Mosca, Hooper and Moffat, but that stretch of road doesn't impress me with the memory of trees much. Just a few in each town.
Monte Vista does seem to have a row of double trees on its eastern side along Hwy 160, and although there are homes around currently, 50 years ago this area may have been fields.
Try Google Maps for some good, detailed, close-up satellite shots:
http://maps.google.com/maps
^..^ Julie