Report 36727: Biologist observes a biped on a ridge outside Missoula

While horseback riding one afternoon or late morning, I observed a large, black upright creature that was walking along and just below a ridge to the east of me.  As I my horse and I continued to climb up the hill to get a better vantage, the creature apparently realized it had been seen or saw us, and ran back in the direction from which it came.  It was very tall and black.  I thought it was a bear at first, but it was upright and extremely fast as it ran.