Fountain Formation

What the map says

Reddish-brown arkosic conglomerate and pebbly sandstone containing thin layers of dark reddish-brown shales. Forms red spines and monuments at Red Rocks and Roxborough Parks and flatirons west and southwest of Boulder. Thickness 512 to 610 m.

1:100,000 sheet: Trimble and others, 2003, U.S. Geological Survey Geologic Investigations Series I-856-H (20 crags). A contact line at that scale is about 100 m wide on the ground.

Maroon and red, arkosic, thick-bedded, coarse-grained to pebbly, cross-bedded fluvial sandstone and conglomerate containing thin layers of dark-maroon, hard (siliceous), micaceous siltstone and silty, fine-grained sandstone. Coarser beds commonly fill shallow channels. Sandstone locally bleached light tan to white. Clasts are well rounded to subrounded, as long as 25 cm, and composed mostly of Proterozoic rocks. Scott (1972) reported rare lower Paleozoic clasts in lower part of formation in Morrison 7.5-minute quadrangle. Thickness in quadrangle about 600 m; in Eldorado Springs quadrangle a measured section is 305 m thick (Wells, 1967). Mapped only in Denver Basin

1:100,000 sheet: Kellogg and others, 2008, USGS Geologic Investigations Series 3000 (27 crags). A contact line at that scale is about 100 m wide on the ground.

Moderate reddish-brown, iron oxide stained, interstratified arkosic conglomerate and moderately coarse-grained, feldspathic sandstone containing thin layers of dark reddish-brown to purplish shale; thickness varies from 210-480 m. Measured section near L

1:100,000 sheet: Colton, Roger B., 1976, U.S. Geological Survey Geologic Investigations Series I-855-G (43 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.