Casa Caldera is an off-grid house located in a remote landscape on the southwestern bajada of the Canelo Hills in Southern Arizona’s San Rafael Valley, two hours southeast of Tucson and 15 miles north of the US/Mexico Border. Siting is balanced between the prospect of the open range and distant mountains toward the west and refuge from those who may venture across the landscape. Proximity to the border and immigrant related foot traffic led the owner to request an impenetrable structure. The house emerges from the native grasses, Emory Oaks, and open ranges beyond, in a simple monolithic rectangular form of 18” mass walls constructed of poured lava-crete. The material is comprised of a mixture of pulverized lightweight red scoria, cement, and water, rammed into formwork. These walls create the structure, finish and offer insulation and thermal mass all in one stroke. The 945 sq ft structure is a reinterpretation of the regional vernacular “zaguan” housing typology. The plan locates two bedrooms of 265 sq. ft. opposite a living room, also 265 sq. ft., separated by a 270 sq. ft. zaguan space running between them. Large bi-fold doors on the ends of the zaguan connect the space to the outside, introducing natural light when open, and security when closed. Cooling is provided by natural cross ventilation through the zaguan and window openings, while wood fuel sourced on the property provides heating. Water is from a well, while solar power is used for minimal electrical and appliance needs. Casa Caldera is almost entirely custom built. The scoria walls, steel windows, doors, hardware, leather pulls, wood siding, millwork, casework and framing were all fabricated and installed by DUST. The wood used on the ceiling and Zaguan wall is sassafrass. A single 30-yard roll-off of waste was removed after the entire construction process.