The base of the wedge is approximately along a line from the Arizona-New Mexico border southwest of Gallup, New Mexico to east of Cookes Range, where the overlying Pescado or D-Cross Tongue of the Mancos Shale pinches out.

The wedge itself pinches out along an arc that passes south of Gallup and just north of Acoma Pueblo and west of Capitan.

[1][3] The base of the formation contains the ammonite Spathites coahuilaensis characteristic of the middle Turonian.

[4] The formation spans the ammonite zones of Collignoniceras woollgari, Prionocyclus percarinatus, P. hyatti, and P. macombit, indicating that the formation ranges from early middle Turonian to early late Turonian.

[5] In 1983, Hook et al. raised the unit to formation rank and interpreted it as a clastic wedge directed to the northeast into the Mancos Shale.