Silica plugs and collapse features occur south and west of the Cameron mining district. The plugs are sharp, dark cones which resist erosion and rise up to 100 feet above the surrounding Plateau strata. They are believed to have been formed by the precipitation of silica from hypogene solutions ascending along vertical conduits. Silica-cemented cores contain breccia fragments, conglomerate pebbles, indurated shale fragments, and coarse sand grains.
Collapse features in association with uranium mineralization contain silicified breccia, bleached strata, and argillic alteration. These are attributed to the activity of rising thermal solutions which caused localized collapse in the Permian Kaibab Limestone and overlying Triassic formations by the removal of carbonates.
Examination of the mineralization associated with the plugs and collapse features indicates the introduction of U, Cu, S, P, Si, Fe, and Mn. Most of the features are radioactive. Both types of structures are believed related to centers of hydrothermal activity and suggest an original hypogene source of uranium.