Pending. The accident pilot departed Rifle, Colorado (KRIL) with his two sons in very marginal weather conditions, and flew southeast at approximately 10,000 feet MSL. Just before terrain collision, the flight track shows a course reversal to a northwest heading, likely due to IMC conditions and/or airframe icing, where the aircraft did impact rising terrain near Pass Creek. The aircraft had previously successfully navigated the pass southeast bound between Anthracite Range and Storm ridge. There were two adults and one child on board, no survivors.