Haageocereus australis

Haageocereus australis, commonly known as 'Quisco De La Costa De Aric', is a species of cactus endemic to southern Peru and northern Chile. Flower color is white. It is hardy to USDA Zone 10b and grows in a very dry desert. The stems grow along the ground and may reach in length.
References.
"The Cactus Family" by Edward F. Anderson, Wilhelm Barthlott, Roger Brown