By 1860, Steen was posted in Oregon. On 28 March of that year, General William S. Harney ordered him to lead an expedition from Fort Dalles to Harney Lake, a distance of . Steen's party followed the Walla Walla road to the mouth of the Deschutes River. He then turned south passing through the Ochoco highlands and the Trout Creek area before exploring the upper Deschutes River country. Near Pilot Butte, Steen turned east toward Harney Lake conducting road survey work along the way. While en route, another Army survey party led by Captain Andrew J. Smith was attacked by Indians north of Harney Lake. Steen immediately abandoned his survey work and proceeded to the Harney Lake where he joined Smith and his party. To protect the survey teams in the area, Steen established Camp Union on Silver Creek, north of Harney Lake.