Minus -17 the coldest in Denver, EVER?
Whoa!
I can remember some -20's in Central Utah when I was growing up, and that was at 4500'.
The only sink I recall was the Randolf Sink in the Wasatch Range, which usually gets REALLY cold ~~ -20 is "normal" for that place.
I remember -20F in Michigan, with high winds and a mile walk to school. They didn't calculate wind chill in those days, all I knew was... it... was... cold!