[2] The formation, deposited in a calm near-shore lagoonal brackish environment, with possibly fluvial influence, has provided a rich assemblage of fossil crocodylians, turtles, giant sloths and various types of fish.

The Castillo Formation crops out cover a wide semicircular area that extends through the northwestern Venezuelan states of Falcón and Lara.

During Oligocene to Miocene times, the formation formed the northwest to southeast edge of the Falcón Basin.

The formation was deposited in a calm near-shore marine to brackish lagoonal environment with possibly fluvial influence.

[5] Elements of the fauna are consistent with the hypothesis that a tributary and/or delta of the Orinoco existed in this area of northwestern Venezuela during Early Miocene times.