Geologic units in Susquehanna county, Pennsylvania

Catskill Formation (Devonian) at surface, covers 85 % of this area

Grayish-red sandstone, siltstone, shale, and mudstone; units of gray sandstone occur in upper part; lithologies in upper part arranged in fining-upward cycles. In the Altoona area, the Catskill Formation is mapped as the Duncannon, Sherman Creek, and Irish Valley Members, which are described under "Central and Eastern Pennsylvania" provinces.

Lock Haven Formation (Devonian) at surface, covers 11 % of this area

Interbedded olive-gray mudstone, siltstone, sandstone, and thin conglomerate; marine fossils throughout; "Chemung" of earlier workers. Laterally equivalent to Scherr and Foreknobs Formations.

Catskill Formation (Devonian) at surface, covers 4 % of this area

Succession of grayish-red sandstone, siltstone, shale, and mudstone, generally in fining-upward cycles; some gray sandstone and conglomerate.

Pottsville Formation (Pennsylvanian) at surface, covers 0.2 % of this area

Gray conglomerate, fine- to coarse-grained sandstone, and siltstone and shale containing minable anthracite coals. Includes three members, in descending order: Sharp Mountain--conglomerate and conglomeratic sandstone; Schuylkill--sandstone and conglomeratic sandstone; Tumbling Run--conglomeratic sandstone and sandstone.

Llewellyn Formation (Pennsylvanian) at surface, covers < 0.1 % of this area

Gray, fine- to coarse-grained sandstone, siltstone, shale, conglomerate, and numerous anthracite coals in repetitive sequences.

Gardeau Formation (Upper Devonian) at surface, covers < 0.1 % of this area

Shale, siltstone; Roricks Glen Shale.

Upper Walton Formation (Upper Devonian) at surface, covers < 0.1 % of this area

Shale, sandstone, conglomerate.

New Milford Formation (Upper Devonian) at surface, covers < 0.1 % of this area

Sandstone, shale.