It preserves fossils showing it was deposited in the middle to late Pennsylvanian.

[1][2] The Bar B formation is mostly cyclic[2] beds of shale and limestone, with shale making up about 80% of the formation and limestone the other 20%.

[1][2] The formation contains abundant bryozoan fossils.

[3] The formation was first defined by V.C.Kelley and Caswell Silver in 1952.

[3] Bachman and Myers criticized its definition in 1975,[1] but it is accepted by Kues and Giles, though they restrict it to the Caballo Mountains.