It was laid down in marshy delta conditions, with poor drainage and frequent flooding, under a warm, humid and seasonal climate.

The underlying Pictured Cliffs is a marginal marine sandstone, deposited in an environment similar to offshore barrier islands of the southeast United States.

As the seaway retreated, the Pictured Cliffs was covered by the Fruitland Formation, which was deposited in near-shore swampy lowlands.

An ash bed lying above the upper boundary with the Kirtland Formation has been dated to 75.02 ± 0.13 Ma ago.

The Fossil Forrest member is considered to be part of the Hunter Wash, fauna shared with the overlying lower Kirtland Formation.