On August 14, 1848, the Oregon Territory was established. American ships reached the Oregon coast in 1788. In 1792, Captain Robert Gray, an American, was the first European to explore the Columbia River. Gray named the river after his ship. The Lewis and Clark Expedition traveled by land to the mouth of the Columbia River in 1805. These explorations gave the United States solid grounds for claiming the Oregon region. In the early 1800s, the Oregon region was defined as stretching from Alaska, which was controlled by Russia, to California, which was ruled by Spain. Oregon’s eastern boundary extended all the way to the Rocky Mountains. Russia, Spain, Great Britain, and the United States all made claims on this area.