Hetch Hetchy Railroad Engine No. 6 is a three truck Shay locomotive, built by the Lima Locomotive Works in 1921. Based on a 19th Century invention of Ephriam Shay, this engine was designed to negotiate steeper grades and sharper curves than is possible with a conventional rod design steam railroad locomotive. This locomotive was the last and largest purchased by the Hetch Hetchy Railroad, and the only Shay locomotive it owned, although a number of leased Shay locomotives were used on the line at different times.

Hetch Hetchy Railroad Engine No. 6 went to work in the spring of 1922 on the slow haul of cement trains up the steep grade known as Priest Hill during construction of the Hetch Hetchy Project. The Hetch Hetchy Railroad was owned and operated by the City of San Francisco. It extended 68 miles from Hetch Hetchy Junction on the Sierra Railroad through Groveland to the site of construction of O'Shaughnessy Dam in the Hetch Hetchy Valley in Yosemite National Park.

The Hetch Hetchy Railroad was built to haul construction materials for the dam and other portions of the Hetch Hetchy Project, an engineering project of regional historical significance designed to impound water in the Sierra Nevada and transport it across the Central Valley of California and the Coast Range to San Francisco and to produce hydroelectric power in the transportation of the water. Construction of the dam itself proceeded from 1915 to 1922, and its height was raised between 1934 and 1938. The railroad was begun in 1914 and scrapped in 1950.

Upon completion of that phase of the Hetch Hetchy project, the locomotive was put up for sale in 1925 and purchased by the Pickering Lumber Company over whose standard gauge logging railroad it operated sporadically for many years until retired from service in 1958. It was subsequently moved to a National Park Service transportation exhibit at El Portal.

The Pickering Lumber Company Railroad on which this locomotive operated after its sale by the Hetch Hetchy Railroad was a logging railroad which began operation as the Sugar Pine Railway, Pickering being its later name. It was headquartered at the lumber company town of Standard.

Excerpted from the NRHP nomination.