It is typically composed of alternating marls and limestones with thin volcanic ash beds (bentonites).

It was named for outcrops near the former Boquillas post office in Big Bend National Park.

[2] The term Boquillas Formation has been used for rocks that outcrop from Del Rio, Texas to as far west as Doña Ana County, New Mexico.

[3] Vertebrate fossils found in the Boquillas Formation include mosasaurs, fish bones, and shark's teeth.

[4][5] Invertebrate fossils found in the formation include ammonites, swimming crinoids, inoceramid clams, sea urchins, oysters, and foraminifera[1]