Further paleomagnetic results from Precambrian formations of the western United States are described. The Sioux and Barron quartzites from Minnesota and Wisconsin, the Uinta Mountain Group from Utah, and the Apache Group from southern Arizona give poles in the east-central equatorial Pacific similar to those of the Grand Canyon Series from northern Arizona and the Belt Series from Montana. There is evidence that the rate of polar wandering varies with geological time, being least in the interval between 600 million years (m.y.) and 1000 m.y. This suggests a quiescent period in orogenic activity as is also indicated by the distribution of ages of metamorphic and igneous rocks. A comparison of these pole positions and those for Keweenawan rocks possibly suggests relative motion within the continent of North America.

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