English: Founded during World War II, the Air Corps Jet Propulsion Project (ACJP Project), a project of the Guggenheim Aeronautical Laboratory of the California Institute of Technology (GALCIT), was an organizational forerunner to JPL. The ACJP Project built a series of adjoining sheds and buildings called "The Gulch" in the Arroyo Seco. In the Gulch, ingredients for solid and liquid fuel rockets were stored and prepared.

The Project allowed no smoking in the Gulch. Twelve-inch high orange-on-white signs marked with the letter "C" designated the area. This meant that no more than 1000 pounds of explosives could be stored in any building at one time. The Gulch may have been so named because of the slight hillside depression in which it lay. Or it could have been because of the name of the most likely place for a cowboy ambush, as dramatized in radio shows of the 1940's. The Gulch was rightfully considered a dangerous place by many JPL employees. This photograph was taken at the entrance to The Gulch, looking toward the southeast and showing the corridor between the sheds. The rooms and sheds faced each other in two parallel rows that ran roughly north and south between present-day JPL Building 103 and Explorer Road. The buildings had protective earth berms to both the east and west. They had cement floors, walls made of lath and plaster or railroad ties, and barricades made of railroad ties outside each open-face room.

By August 1948 JPL's needs had changed; the usefulness of The Gulch was over. JPL tore down the Gulch and replaced it with trees and a parking lot.