The banded iron is of the Algoma variety, formed by local volcanism rather than in the Great Oxidation Event.

[8] Based on gravity measurements, the dense rock of the complex may extend in the subsurface well to the north and east into the San Juan basin.

[9] The Moppin Complex is intruded by plutonic rocks, including the Maquinita Granodiorite, the trondjhemite of Rio Brazos,[3] dikes and sills of the Burned Mountain Formation,[10] the Tusas Mountain Orthogneiss, and the Tres Piedras Orthogneiss.

[12] The unit is interpreted as a portion of an island arc accreted to the southern margin of Laurentia as part of the Yavapai Province between 1.8 and 1.755 Gya.

[15] The rock beds making up the Moppin Complex were originally named the Hopewell Series in by Evan Just in 1937 during an investigation of pegmatites in the Tusas Mountains.