Geologic units in Treasure county, Montana

Additional scientific data in this geographic area

Lance Formation (Cretaceous) at surface, covers 30 % of this area

Orangish brown, coarse- to fine-grained sandstone with subordinate interbeds of shale and mudstone. Laterally equivalent to Hell Creek Formation. Fluvial. Thickness as much as 150 m (492 ft).

Bearpaw Formation (Cretaceous) at surface, covers 20 % of this area

Dark gray shale with several zones of calcareous concretions, a basal zone of ferruginous concretions, and numerous thin bentonite beds. Marine. Thickness as much as 300 m (984 ft).

Tullock Member of Fort Union Formation (Tertiary) at surface, covers 14 % of this area

Yellow sandstone interbedded with subordinate grayish brown and black shale and thin beds of coal. Alluvial plain. Thickness as much as 180 m (590 ft).

Lebo Member of Fort Union Formation (Tertiary) at surface, covers 11 % of this area

Dark gray carbonaceous shale, bentonitic claystone, sandstone, and coal. Alluvial plain. Thickness as much as 185 m (607 ft).

Alluvium (Quaternary) at surface, covers 10 % of this area

Gravel, sand, silt, and clay deposits of stream and river channels, and floodplains.

Gravel (Quaternary) at surface, covers 6 % of this area

Variable deposits that range from pebble to boulder size and include sand, silt, and clay. Dominantly alluvial terrace, abandoned channel and floodplain, remnant alluvial fan, and local glacial outwash.

Tongue River Member of Fort Union Formation (Tertiary) at surface, covers 6 % of this area

Yellowish orange sandstone, sandy and silty carbonaceous shale, and coal. Alluvial plain. Thickness as much as 300 m (984 ft).

Fox Hills Formation (Cretaceous) at surface, covers 1 % of this area

Yellowish orange to gray, fine- to medium-grained, non-calcareous sandstone in upper part, and interbedded sandstone, siltstone, and black shale with calcareous concretion zone in lower part. Marginal marine. Thickness 30–45 m (98–148 ft).

Gravel (Quaternary and Tertiary) at surface, covers 0.8 % of this area

Variable deposits that range from pebble to boulder size and include sand, silt, and clay. Dominantly alluvial terrace, abandoned channel and floodplain, remnant alluvial fan, and local glacial outwash.

Judith River Formation (Cretaceous) at surface, covers 0.7 % of this area

Light brown to light gray, fine- to coarse-grained sandstone with interbeds of gray to black carbonaceous shale, silty shale, and thin coal. Local Parkman Sandstone Member (lower part of formation):yellowish gray to brownish gray and olive green, fine- to medium-grained, cross-bedded sandstone interbedded with yellowish gray, silty shale. Estuarine, brackish, and nearshore marine. Thickness as much as 305 m (1000 ft).