You can find examples of unmowed yards that are still beautiful and functional in many desirable urban-residential areas of cities. I'm thinking particularly of Hyde Park in Austin, Somerville in the Boston metro, Capitol Hill in Denver, Burlington VT, and much of Portland OR. It's not until you hit the suburbs where HOAs have dug in their claws and stand in the way of "cookie-cutter" ever becoming anything but.

In Colorado, check out the Colorado Native Plant Society or the Colorado Cactus & Succulent Society. Denver Botanic Gardens is also wonderful with outreach and education efforts, but they're not strictly focused on native plants (as far as I know).