The most important in terms of production and size are the Rocky Mountain coalfields in the Foreland Belt.
(The most important in terms of production and size; are; the Rocky Mountain coalfields in the Foreland Belt) Context(The most important in terms of production and size are,List([0, 54))):(the Rocky Mountain; coalfields; L:in the Foreland Belt)
The most important in terms of production and size are,List([0, 54))
The most important in terms of production and size the Rocky Mountain
are coalfields
the Rocky Mountain coalfields in the Foreland Belt
L:in the Foreland Belt