Well, I'm a few decades too late... I grew up in Monte Vista. I remember finding a lot of arrow heads up in the San Juans.
Just out of curiosity, have you ever been detecting at the Sand Dunes? I can't imagine what you'd come across there -- mostly garbage left by visitors, but can't help but wonder if the seasonal "river" would wash anything good down from the mountains.
That's on my "to do" list. Not sure if the park rangers would like me poking around on government land though!! Medano creek (the seasonal river) is kinda dirty right now. The had a fire up in the Sangre De Cristo mountains where it starts and it burned for well over a month. I have a friend who keeps finding arrow heads (and really old sharks teeth!!) down south of Manassa. I'll be checking out the old Blanca River bed and streams leading into it with my Gold Bug S.E. soon.....it's on my property so I don't have to worry about permission. I'll post pics if/when I find anything.