Initial extrapolations placed Cooper's landing zone within an area on the southernmost outreach of Mount St. Helens, a few miles southeast of Ariel, Washington, near Lake Merwin, an artificial lake formed by a dam on the Lewis River. Search efforts focused on Clark and Cowlitz counties, encompassing the terrain immediately south and north, respectively, of the Lewis River in southwest Washington. FBI agents and sheriff's deputies from those counties searched large areas of the mountainous wilderness on foot and by helicopter. Door-to-door searches of local farmhouses were also carried out. Other search parties ran patrol boats along Lake Merwin and Yale Lake, the reservoir immediately to its east. No trace of Cooper, nor any of the equipment presumed to have left the aircraft with him, was found.