Wolf, Tom & Sparks, Barbara (1995) Colorado's Sangre de Cristo Mountains, University Press of Colorado, p. 157

In their dual capacity as foresters and wildlife officers, the rangers of the 1920s and 1930s kept meticulous records that make riveting reading ... An early supervisor wrote:

On several occasions this summer, Ranger Paul Gilbert has discussed with me the matter of there having been found in Lily Lake, in the southern end of Blanca district, from two to four or five "Duck-bills." I have not been anxious to report this earlier, thinking that some mistake might have been made in the identity of these mammals. However, on my last trip to his station, and in a a trip over his district, I found that the existence of the mammals is known to several men and that several men are making an attempt to trap them. As I understand it, these are egg-laying, burrowing, aquatic mammals and are supposed to exist largely, and possibly only, in Australia. I have read somewhere that North America has none of these mammals, and if this be the case, I think the matter should be immediately investigated by someone from the Smithsonian Institute, or someone who might report their existence to the proper authorities.

In vain, Ranger P. Gilbert tried to trap the elusive duckbills for a few years. Not a man to ignore procedure, he even obtained a trapping permit from the State Game Warden in 1924. The earnest Gilbert wrote, "I am of the impression that there is absolutely no chance for mistake in this since I am acquainted with marten, marmot, groundhog, and fox tracks, when I see them. The tracks of the platypus will, if found in fresh mud, show the indentation of the webs that are between the toes."

Unfortunately for today's Lily Lake, the years 1927-1930 brought no new sightings. And then the record falls silent, except for a politely sceptical letter from an Australian journalist dated June 15, 1931.