John Colter may have been the first easterner to visit the pass in 1807, but this is based on circumstantial evidence and is disputed by scholars. Wilson Price Hunt, the Astorians overland to the mouth of the Columbia reported crossing Union Pass on September 15, 1811. This is the first record of the pass. The expedition guides were Edward Robinson, John Hoback and Jacob Rizner. Their previous participation in 1809 with the Henry expedition to the source of the Missouri River and back by way of the Green River it is accepted that the three had been through Union Pass, during the year 1810.