This note extends the gravity terrain corrections for elevation differences beyond the tables originally published by Hammer (1939). Experience in the Rocky Mountain area has demonstrated to us the need for such an extension. The frustration encountered by the authors led to a computer program to calculate the terrain correction tables presented in this article. The mountain topography in western Montana is typical of an area not sufficiently regular to allow use of the less tedious inclined-plane model presented by Sandberg (1958). The inclined-plane and the cylinder models are designed for calculating the effects of local terrain and do not include a correctional factor for earth curvature. Large regional surveys require the Hayford- Bowie terrain correction zones. However, local surveys can be easily incorporated into these larger studies by Hammer to Hayford-Bowie transition tables (Sandberg, 1959),

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