For hundreds of years, Native Americans in the Southwest built their dwellings of earthen blocks, or adobes, and later settlers maintained and adapted these construction techniques. Though promoted by the U.S. government as a low-cost residential construction method in the 1920s and '30s, adobe was almost completely supplanted by frame and stucco housing after about 1970. Today, however, with interest in earth-friendly construction growing, many people are paying closer attention to these regional traditions. This phenomenon has led to a resurgence of both adobe masonry and its cousin on the concrete side, rammed earth (moist soil cement compacted into formwork in layers). According to Michael Moquin, editor of Adobe Journal, there are about 200,000 modern homes in the U.S. made of adobe or rammed earth, 97% of them in the Southwest. Like other masonry materials, adobe absorbs heat and stores heat energy. During the day, thick adobe walls absorb heat energy from the sun, preventing the interior space from overheating. At night, when the outside temperature drops, heat stored within the wall is released, helping to maintain a constant, comfortable temperature indoors.