Light beam in Upper Antelope Canyon was formed by erosion of Navajo Sandstone, primarily due to flash flooding where during monsoon season, rainwater runs into the extensive basin above the slot canyon sections, picking up speed and sand as it rushes into the narrow passageways. Over time the passageways are eroded away, making the corridors deeper and smoothing hard edges in such a way as to form characteristic 'flowing' shapes in the rock.