Photograph of the Travel Oil and Gravel Mixer trucks during the construction of an aqueduct, 1933. At left, a large tractor is visible with treadwheels, pulling a metal frame which a man attends to, as well as a small tank. This caravan is followed closely by a small tanker truck. Mountains and desert are visible in the background.; Note with negative reads: "This is only a part of the great mass of machinery in building the aqueduct and supplementary improvements. This road machine mixes gravel and oil as it travels. It is being used in building a part of the 125 miles of desert oil-gravel highway along the route of the aqueduct. The road is necessary for hauling materials and gives access to the aqueduct".