A log flume is a flume specifically constructed to transport lumber and logs down mountainous terrain to a sawmill by using flowing water. These watertight trough-like channels could be built to span a long distance across chasms and down steep mountain slopes. The use of log flumes facilitated the quick and cheap transportation of logs and thereby eliminated the need for horse- or oxen-drawn carriages on dangerous mountain trails.
Early flumes were square chutes that were prone to jams that could cause damage and required constant maintenance. In 1868, James W. Haines first built the "V"-shaped log flumes that allowed a jammed log to free itself as the rising water level in the flume pushed it up. These efficient flumes consisted of two boards, 2 feet (0.61 m) wide, joined perpendicularly, and came in common use in the western United States during the late 19th century.
The longest log flume was reputedly the Kings River Flume in Sanger, California. Built in 1890 by the Kings River Lumber Company, it spanned over 62 miles (100 km) from the Sierra Nevada to the lumber yard and railroad depot in Sanger. Together with a constant water supply from a nearby reservoir, the flume enabled the efficient transportation of boards of lumber over deep gorges and cliffs and thereby opened up the area now known as Sequoia National Forest for clearcutting of the giant redwood forests. Proper operation was ensured by "flume herders" who at various locations along the flume checked the flow of lumber and water.
On occasion, despite being exceedingly dangerous, flume herders and others would ride down the flume in small craft or boats, either for inspection or for thrills. Such rides were the precursor of the modern log-ride amusement park attractions.