There are some variations to this route, but this was the standard long run for CU and the snooty Boulder effete locals. :) Runners park and run from slightly before (100') the 5-mile mark to across Peak-to-Peak Hwy. 72, about 1.5 or 1.6 miles to the campground and dead-end and came back. It's 17.3+ miles by the measuring wheel, though they call it "17".
I remember breaking 59 at the turnaround and being psyched (58:40s), and 52:40s or so coming back, give or take 10 secs. I'm now 40 (41 in Sept.), so this was in fall 1994-fall 1995 range when I had the desire and ability to train that hard. I did 14 up there on July 4th at a significantly slower pace and it killed me.
As for my specific mile splits, I don't recall those too well. I remember a close to 5-flat mile (stupid?) on the return run, flying down from the 9-mile marker to the 8-mile marker, and a 7:20 or so struggle on this stretch as the slowest mile going out (from 8 to 9). ... But it's just about all downhill (west) or uphill (east).
The rest of the miles likely ranged from 5:40-6:40s. One time, I was pretty toasted at the end. Another time, I felt like I could run five more miles. Possibly one of the best training days opf my life.