As gold extraction became more complex, the demand for water increased. The Golden Rock Water Company employed mostly Chinese laborers to ditch water from the Middle and South Forks of the Tuolumne River to a dam near Hardin's Mill. A gravity flow wooden flume was required to transport the water over Conrad Gulch.

The flume was built of sugar pine and had eleven towers, the highest being 265 feet. The bases of the towers were 50 feet square, tapering together towards the top. The end of one post rested on another. The flume box was 250 feet high from the deepest point in the canyon and was six feet wide and four feet deep.

The first water ran through the 36 mile ditch March 29, 1860 and continued for 9 years supplying water for miners in Garrote, Big Oak Flat, Moccasin Creek and nearby areas.

In 1868 the flume fell to the ground with a tremendous crash. Andrew Rocca, the new owner, immediately set out to replace the vital part of the water ditch. The iron sheets for the pipe were brought from San Francisco up the San Joaquin River to Stockton and by horse teams to Mariposa County. The pipe was put together on the ground and had water running through it in two months.

The low cost and short amount of time it took to construct the pipe may be attributed to the cooperative labor of approximately two thousand miners from Mariposa and Tuolumne Counties who forgot their ongoing rivalry long enough to construct the badly needed crossing. Their livelihood depended on the water running through the ditch.

The Golden Rock Water Company did well until Rocca sold out in 1875. After this, the ditch was owned by several large mining companies.

In 1905 the ditch was acquired by Big Creek Gold Mining Company which later became the Tuolumne River Power Company. They planned to use the ditch for mining, timber, and electrical power.

From 1917 to 1923 the ditch was owned by the City and County of San Francisco as a supply for their railroad and buildings along with fire protection for the town of Groveland.

Slowly the ditch lost importance, especially after the O'Shaunessey Dam (Hetch Hetchy) was built. Finally in 1942, Tuolumne County bought the ditch for $750.00 of accumulated delinquent taxes.

Presently [1975], little remains of Big Gap Flume.

Adapted from the 1975 NRHP nomination.