Pritchard's CO Book says Cronin's Saloon - 1915. He lists other from Dan Cronin at a couple of Denver addresses including 2060 Champa which is probably at the corner of 21st & Champa. On one of those, the books says The Oak Saloon - 1904-15, so presumably this one is toward the end of that period. In 2004 he had noted 4 examples of the one you have.
John in ID