A high-quality tea Mark’s passed up in Coloradan town (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

AN ASSAM (tea from the Assam region of India: I suppose “high-quality” in that it’s a single-origin tea rather than a blend?), with the M (abbreviation for mark, as in the former German currency Deutsche Mark or DM) moved to the start (passed up, in a down clue). Well, it’s a town in Colorado, but I hadn’t heard of it.