The Wellington coal bed was deposited in a rapidly subsiding and seismically active forearc basin of Late Cretaceous age, situated along the Pacific margin of North America. Coal-forming peat accumulated atop a complex of nearshore marine sand bars, into which meandering streams were incised. Thick peats with numerous lenses of organic-rich mud were deposited in the channels, while thinner peats were deposited over the bars and between the channels.

The location of stream channels, and hence of thick peats, was influenced by movements along faults, which produced scarps at the sand surface. During and subsequent to peat accumulation, streams produced channel scours and overbank flood deposits within the peat, resulting in a complex pattern of splitting and rejoining, which is characteristic of the Wellington coal bed. The position of these streams was controlled by renewed fault movements and by differential compaction over older fluvial deposits within the peat.

Detailed mapping of coal bed sections exposed in colliery workings is required to adequately predict the occurrence and extent of coal bed splits in advance of mining. Recognition of the orientation and frequency of the controlling faults is critical to the prediction of mining conditions and coal quality.