In 1980-81 The late Jack Thode arranged to have several hundred obsolete drawings (these were the original ink on linen drawings) transfered from the D&RGW to the Western History Collection of the Denver Public Library. Most of these were narrow gauge.
As I recall, about the time that Augie Mastroguiseppe died, there was an additional transfer from the Denver Model Railroad Club collection of several hundred, perhaps even more than a thousand, more drawings. I don't know if this later collection has ever been completly cataloged.
Dave g