The predominantly mudstone formation dates to the Late Cretaceous period; Turonian and Cenomanian epochs, and has a maximum thickness of 693 metres (2,274 ft).

The formation was defined and named in 1991 by Ulloa and Rodríguez after Simijaca, Cundinamarca.

[1] The Simijaca Formation is characterised by a sequence of mudstones, grey and black shales with sandstone and limestone intercalations.

[5] The formation has been deposited in an open marine platform setting.

[7] The Simijaca Formation is apart from its type locality in the Quebrada Don Lope,[2] found at surface in the north of the Bogotá savanna, in the Tabio anticlinal, along the road Ubaté-Carmen de Carupa,[8] at the western and eastern flanks of the Aponsentos-Chiquinquirá Synclinal,[9] near Tena, south of Anolaima and Cachipay,[10] and between Anapoima and Granada.