The formation crops out in the San Juan Mountains of Colorado[1] but may be present in the subsurface over a much wider region,[2] including the Paradox Basin.

It was assigned to the Cambrian by Charles Whitman Cross and A.C. Spencer in 1899, when they first described the formation,[5] and was thought to correlate with the Tintic Quartzite and the Tapeats Sandstone.

[6][1] The formation is interpreted as sediments deposited in a tide-dominated estuary setting during a rise in sea level (a transgression).

At least three paleovalleys have been identified in the underlying Precambrian rock that are filled by the Ignacio Formation.

These are up to 30 kilometers (19 mi) wide and over 42 meters (138 ft) deep and run from southeast to northwest.