Yellowish orange sandstone, sandy and silty carbonaceous shale, and coal. Alluvial plain. Thickness as much as 300 m (984 ft).
Gray and brown shale, siltstone, silty or bentonitic claystone, sandstone, and coal. Alluvial plain with marine-influenced tongues. Thickness as much as 230 m (755 ft).
Light gray, bentonitic claystone that alternates with gray to brown sandstone interbedded with carbonaceous shale. Laterally equivalent to Lance Formation. Fluvial and flood plain. Thickness as much as 335 m (1,100 ft).
Dark gray, partly silty shale with abundant bentonite beds and zones of gray, calcareous concretions. Marine. Thickness as much as650 m (2,133 ft). Only upper 50 m (164 ft) exposed.
Gravel, sand, silt, and clay deposits of stream and river channels, and floodplains.
Timber Lake Member (Kftt): Yellowish orange to gray, fine- to medium grained, noncalcareous, hummocky-bedded sandstone. Thickness 15–22 m (50–72 ft). Trail City Member (Kftc): Yellowish orange, wavy-bedded siltstone and black shale with calcareous concretion zone. Thickness 10 m (33 ft).
White to yellowish, fine- to medium-grained, porous sandstone. Brackish to marine shoreline. Only present near Glendive (eastern Montana) and in several other isolated areas. Thickness 0–40 m (130 ft).
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.
Yellowish orange or tan, fine- to medium-grained sandstone interbedded with mudstone and thin shale and coal beds. Estuarine. Thickness as much as 55 m (180 ft).
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.
Gray sand, silt, clay, and sandstone; river sediment; as thick as 150 metres (500 feet).
Dark-gray shale; marine offshore sediment; as thick as 700 metres (2,300 feet).
Olive-brown sand, shale, and sandstone; marine shoreline and off-shore sediment; as thick as 120 metres (400 feet).
Grayish-brown and yellowish-brown silt, sand, clay, sandstone, and lignite; river, lake, and swamp sediment; as thick as 100 metres (300 feet).
Clay to boulder-size clasts with locally abundant organic material. Thickness up to 75 ft (23m).
Tan to brown, light- to dark-gray, "somber beds" of shale. Interbedded with brown to red carbonaceous shale, gray and brown bentonitic silty shale, and gray, brown and yellow siltstone, sandstone, and claystone-pebble conglomerate. Thickness 260-600 ft (79-183 m).
White, tan, yellow, and gray, cross-bedded, fine- to medium-grained,silty sandstone interbedded with locally bentonitic, gray siltstone, claystone, and sandy to silty claystone. Characterized by uranium-bearing lignite beds and "clinker" beds fromed by burning coalseams. Thickness up to 420 ft (128 m).
Grayish-brown and yellowish-brown silt, sand, clay, sandstone, and lignite; river, lake, and swamp sediment; as thick as 100 metres (300 feet).
Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).