In the Late Eocene, 35 million years ago, the climate and vegetation were quite different. There were several differences in the regional and continental geography that accounted for those differences. Because of continental drift, Antarctica and South America separated and the circum-Antarctica current developed. This changed worldwide oceanic circulation patterns and resulted in a worldwide cooling trend. Also, the North American Continent has been moving northwestward at the rate of about 1 inch per year. How far has it moved in the past 35 million years? (Colorado was about 600 miles southeast of where it is now).