How close to a river/stream were you? That rock has been rounded by tumbling in a river at some point, which may answer your question.
By Leo Paik Administrator From: Westminster, Colorado Jan 27, 2012
You know, sometimes climbers are a playful bunch that like to mess with other folks and migrate a bit of rock from one area to another just to confound the future visitor...not that any of us have ever done that before.
Actually the rock wasn't near a stream or a river. We found it as sort of a trail marker hiking to the dome I posted that no one has yet to identify. It's just like Evans salt and pepper granite. It was also probably a good 60 lbs or so....
It's a glacial erratic. The rock was scooped up elsewhere and dragged along and relocated by the glacier that carved out Devil's Head, T-Ridge, and left the huge, balanced rock down Rampart Range Road.