Precambrian Paleogeography, Southwestern US

Middle Proterozoic (~ 1.7 Ga) -- This highly speculative reconstruction is based on recent work by geologists at Northern Arizona University and the University of New Mexico

Mesoproterozoic (~1.1 Ga) -- North America was part of the supercontinent Rodinia and was possibly adjacent to Antarctica and Australia

Neoproterozoic (~ 650 Ma) -- North America rifted away from Antarctica and Australia as the Precambrian supercontinent broke up. Western North America began a long history as a passive margin as the continent moved away from a mid-ocean rift zone. Some blocks of rifted North America likely lay off shore, similar to the island of Madigascar off east Africa today

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