The 40th of a series of caches planned to be hidden at or near the historic rural schoolhouses of Routt County (RCSH - Routt County School Houses). See the first cache of this series (GC6QQ71) for a complete and updated list of the ones currently available - but this list will continue to grow as there were 96 schools which served Routt County neighborhoods from 1883 until 1960 when the rural districts consolidated.
The Pine Grove school was located 4 miles north of Columbine on County Rd 129 near Smith Creek. This cache meets all three of those qualifications, PLUS goes with the name of the school, although I don’t know exactly where the school sat. It was a log school that was built in 1921 and operated until about 1937 when the parents in the district (mostly employees of the Turner Sawmill) decided to build a school closer to the Sawmill. The Turner Sawmill and school are marked by another cache in this series (GC6Q8Z1) but is only accessible in the summer unless you have a snowmachine and a shovel! 
Incidentally, the Turner Sawmill cache was the 5th ever cache we hid, long before we started this series – knowing that there was a sawmill there at one time per the evidence - but not knowing any of the history until recently!