Most of the fields in North Dakota were located by a combination of surface mapping and the reflection seismograph. Detailed surface mapping in southwestern North Dakota will be very valuable in locating other structural anomalies; however, the essentially flat Tertiary and Upper Cretaceous beds and the glacial debris north and east of the Missouri River hamper this method of exploration.

Other fields have been located by a combination of seismograph and subsurface studies, and in the future this combination will become a much more valuable method of exploration.

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