Day Fossil Beds National Monument. Most significant among the prehistoric sites are the Picture Gorge pictographs, consisting of six panels of rock art in the canyon at the south end of the Sheep Rock Unit. The art is of undetermined origin and age but is "centuries old". The John Day basin remained largely unexplored by non-natives until the mid-19th century. Lewis and Clark noted but did not explore the John Day River while traveling along the Columbia River in 1805. John Day, for whom the river is named, apparently visited only its confluence with the Columbia in 1812. In 1829, Peter Skene Ogden, working for the Hudson's Bay Company (HBC), led a company of explorers and fur trappers along the river through what would later become the Sheep Rock Unit. John Work, also of the HBC, visited this part of the river in 1831. In the 1840s, thousands of settlers, attracted in part by the lure of free land, began emigrating west over the Oregon Trail. Leaving drought, worn-out farms, and economic problems behind, they emigrated from states like Missouri, Illinois, and Iowa in the Midwest to Oregon, especially the Willamette Valley in the western part of the state. After passage of the Homestead Act of 1862 and the discovery of gold in the upper John Day basin, a fraction of these newcomers abandoned the Willamette Valley in favor of eastern Oregon. Some established villages and engaged in subsistence farming and ranching near streams. Settlement was made more practical by a supply route from The Dalles on the Columbia River to gold mines at Canyon City in the upper John Day valley. By the late 1860s, the route became formalized as The Dalles Military Road, which passed along Bridge Creek and south of Sheep Rock. Clashes between natives and non-natives and the desire of the U.S. Government to populate the region with Euro-Americans led to the gradual removal of native residents to reservations, including three in north-central Oregon: Warm Springs, Burns Paiute, and Umatilla. In 1864, a company of soldiers sent to protect mining camps from raids by Northern Paiutes discovered fossils in the Crooked River region, south of the John Day basin. One of their leaders, Captain John M. Drake, collected some of these fossils for Thomas Condon, a missionary pastor and amateur geologist who lived in The Dalles. Recognizing the scientific importance of the fossils, Condon accompanied soldiers