The area that would become the city of Sacramento was initially observed by many European and American mapmakers as home to Great Plains-based rivers that stretched across the Rocky Mountains and emptied into the Pacific Ocean. Speculation at the time placed the fabled St. Bonaventura River where the American-Sacramento River complex was; mountain man Jedediah Smith mistook the American and Sacramento Rivers for the St. Bonaventura in his 1827 venture into the region, and named the Sacramento Valley the "Valley of the Bonadventure" before trekking southwards along the Stanislaus River.