Dawson Formation and Arapahoe Formation

What the map says

Arkosic sandstone, siltstone, claystone, and (or) minor amounts of conglomerate. Where unit underlies the Denver Formation, it is called the Arapahoe Formation. Where Denver Formation intertongues and pinches out to the south and east, the unit is called the Dawson Formation. Forms most of bedrock between Denver and Colorado Springs. As much as 610 m thick (Scott and Wobus, 1973). A conglomerate at the base of the Arapahoe Formation is an important aquifer in the Denver Area.

1:100,000 sheet: Trimble and others, 2003, U.S. Geological Survey Geologic Investigations Series I-856-H (6 crags). A contact line at that scale is about 100 m wide on the ground.

Served by Macrostrat (CC BY 4.0). The wording is the map's own, quoted as a fact about the mapped unit, not about any one wall.