1966. Historic adobes Between 1937 and 1940 the Civilian Conservation Corps built several adobe buildings to serve as housing and administrative offices for the national monument. The adobe buildings, constructed using traditional methods, continue in use today and are now listed on the National Register of Historic Places. Because of careful conservation, the physical appearance of Casa Grande Ruins has hardly changed since the 1940s. Olmsted shelter In 1932, a ramada to shelter the ruins from weathering was built by Boston architect Frederick Law Olmsted, Jr. In the early 21st century, a pair of great horned owls took up residence in the rafters of the Olmsted shelter. The current protective structure covering the "Great House" replaced a wooden similar structure built to protect it in 1903. Due to the fragile nature of the "Great House," visitors to the site are not permitted inside. To protect its integrity, observation by visitors is only permitted outside the structure. Gallery See also Hohokam Pima National Monument List of national monuments of the United States List of the oldest buildings in Arizona Mesa Grande Oasisamerica cultures Pueblo Grande Ruin and Irrigation Sites References Notes Bibliography External links National Park Service: official Casa Grande Ruins National Monument website Buildings and structures completed in the 13th century National Park Service National Monuments in Arizona Hohokam Archaeological sites in Arizona Archaeological museums in Arizona Museums in Pinal County, Arizona Native American museums in Arizona Native American history of Arizona Archaeological sites on the National Register of Historic Places in Arizona Civilian Conservation Corps in Arizona 1918 establishments in Arizona Protected areas of Pinal County, Arizona Ruins in the United States 13th century in North America Pueblo great houses Casa Grande, Arizona Historic American Buildings Survey in Arizona Works Progress Administration in Arizona National Register of Historic Places in Pinal County, Arizona Ancient Puebloan archaeological sites in Arizona