McDonald Ranch House, Historic ranch house at Trinity Site, New Mexico

The McDonald Ranch House is a one-story adobe building of 1,750 square feet, plastered and painted, with a north-side addition. A low stone wall encloses the 85-by-85-foot site. East of the house stand a divided water storage tank and a Chicago Aermotor windmill; an ice house and underground cistern lie to the west.

The house was built in 1913 as a simple dwelling for a ranching family on the property. In 1945, it took on a different purpose when scientists working on a secret project temporarily used rooms inside for technical work.

The house is named for the McDonald family, who moved into the area in the late 1870s or early 1880s and bought the ranch in the 1930s. They left under protest in 1942, and in 1982 Dave McDonald and his niece Mary staged an armed reoccupation of the ranch. A time capsule buried by Major General Niles J. Fulwyler was opened in 2009, and its artifacts are displayed inside.

The house opens just twice a year for public tours, typically in spring and fall months when temperatures are more comfortable. Visitors should check dates in advance and prepare for desert conditions with appropriate clothing and sun protection.

One room on the northeast side of the house was used for technical preparation work before a major event took place just a couple miles away. The building still bears marks from that intense period when ordinary ranch structures became temporary laboratories.