Although the Spanish began exploring California in the 1700s, it was probably not until Jedediah Smith's expedition in 1827 that Europeans entered the vicinity of the upper American River watershed. Smith's party searched, unsuccessfully, for a way to cross the Sierra Nevada via the American River, though they later did cross the Sierra Nevada via Ebbetts Pass becoming the first non-natives to do so. After the discovery of gold on the South Fork American River at Coloma in 1848, miners soon flocked to the Middle and North Forks as well. Less than two years later, nearly 10,000 miners had staked claims on the Middle Fork, with some of the richest sites including Ford's Bar, Maine Bar, Murderer's Bar and Spanish Bar. During the 1850s, the Grand Flume was built along the Middle Fork from Oregon Bar to Mammoth Bar, dewatering a section of the river bed so it could be turned over for gold. North of the Middle Fork, the Michigan Bluff to Last Chance Trail - one of only a few toll trails in the state - was constructed and used by pack trains of mules carrying supplies to Michigan Bluff, Deadwood and Last Chance.