A dramatic change in the landscape is highlighted in the shaded relief map below. The eastern two-fifths of the state is a relatively uninterrupted plain, while an abrupt change in elevation is obvious to the central and western parts of the state. Spanish Peaks rises 7,000 feet above the western Great Plains and are located at the extreme west edge of the Raton Basin province. It is easy to understand that one of the major rivers in Kansas has its headwaters near Leadville, over 10,000 feet in elevation; the Arkansas River exits Kansas at an elevation of just over 1,000 feet, on its way to the Mississippi River and Gulf of Mexico. According to Kammerer (1990), the Arkansas river is the sixth longest river in the United States, at 1,469 miles (pubs.usgs.gov/of/1987/ofr87-242/).

The Raton Basin is known for the exposed rocks defining the Cretaceous-Tertiary boundary. The Raton Basin transitions into the Southern Rocky Mountains when we cross the Cretaceous Dakota Sandstone hogback into the Lower Permian. This is roughly the same age of rock we left over 500 miles behind in Chase County, Kansas (www.geospectra.net/fieldgeology/kansasrocks.htm).

Colorado Geologic Map generalized-click for a larger view. Image taken
from geosurvey.state.co.us/Default.aspx?tabid=122. To see greater detail,
visit: geosurvey.state.co.us/Default.aspx?tabid=127.

While it is difficult to get much useful information from the geologic map to the left, maps shown below will focus on specific geologic ages and features. The maps are positioned to begin with the youngest rocks at the top and older as you page down. Click on the images to see a larger verson and read more detail at the associated Colorado Geological Survey website.