The rail from Antonito to east of Osier is 70lb put down in 1923 or so. It was second hand rail from the SG mainlines. A lot of it is 1900 and older. In the early 2000's in one of the early track projects, the outside rail on some of the 70lb curves was replaced with heavier relay rail. That is probably what you found at MP 290.

From east of Osier to about a half mile east of the Chama Yard Limit is 85 lb rail put down in 1938. This too was second hand off SG main line somewhere.

The rail west of Chama was all 70 lb. put down in the early 1920's. The Navajo Dam relocation was done with new 90lb rail at the Govt.'s expense.