The major tectonic elements of Central Montana include: (1) the Little Belt-Big Snowy-Porcupine anticlinorium, (2) the northern High Plains region with its igneous intrusions, (3) the Sweetgrass arch, and (4) a southern area that consists of the Crazy Mountain syncline, Lake Basin fault zone, and the northern end of the Bighorn-Pryor uplift. The economic and academic significance of these features and their important subdivisions are reviewed.

The literature is reviewed in an effort to present a picture of the geological development of these tectonic elements. In order to do this, outstanding contributions including those by Erdmann, by Sloss, and by other geologists have been slightly modified by use of new information available at this time. Revised isopach maps and generalized lithofacies maps are presented for central Montana for the Madison-Colorado shale interval.

The effect or significance of certain features or conditions is discussed. These include: (1) the generally positive Sweetgrass arch, (2) the generally negative Beltan (Montana) trough-Big Snowy axis, (3) shallow and deep-seated igneous intrusives of the High Plains, (4) en echelon faults in central Montana, and (5) thrust faulting east of the main Rocky Mountain front.

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