USGS Visual Identifier

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GEOLEX database

Geologic Unit: Middle Park

Publication:
Clark, W.B., 1892, The Eocene of the United States; Interior 
   region: U.S. Geological Survey Bulletin, 83, p. 111-146.
Usage in Publication:
Middle Park beds

Modifications: Geologic Province: Dominant Lithology:
 Named
 North Park basin
 Breccia
 Conglomerate

Summary:
[No type locality or notice of naming a new unit included in report. Only the barest description given.] Occurs in Middle Park, Grand Co, CO in the North Park basin. Is a series of andesitic breccias and conglomerates with interstratified sands as much as 800 to 900 ft thick. Overlying the andesitic beds are sandy shales, sandstones, and grits, chiefly of granitic origin. Seams of lignite material and numerous fossil leaves scattered through the unit. [Sequence of beds not stated.] Rests unconformably on the Cretaceous. Thought to be similar to the Denver formation. Assigned to the Eocene.
Source: GNU records (USGS DDS-6; Denver GNULEX).


Publication:
Izett, G.A., Taylor, R.B., and Hoover, D.L., 1963, Windy Gap 
   Volcanic Member of the Middle Park Formation, Middle Park, 
   Colorado; Article 189, IN Geological Survey research 1962; 
   short papers in geology, hydrology, and topography: U.S. 
   Geological Survey Professional Paper, 450-E, p. E36-E39. 
   [Available online from the USGS PubsWarehouse:  http://
   pubs.er.usgs.gov/pubs/pp/pp450E]
Usage in Publication:
Middle Park Formation*

Modifications: Geologic Province: Dominant Lithology:
 Revised
 North Park basin
 

Summary:
Basal volcanic breccia, volcanic sandstone and conglomerate with andesite fragments that ranges from 0-1,150 ft thick named Windy Gap Volcanic Member of Middle Park Formation from exposures at Windy Gap, Grand Co, CO in the North Park basin. Windy Gap overlies the gray Pierre Shale and underlies an unnamed part of the Middle Park. Upper contact gradational. Windy Gap grades into grits with large amount of Precambrian granite pebbles. Contact usually placed arbitrarily at lowest occurrence of Precambrian granitic rock and microcline fragments. [Overlying parts of Middle Park not discussed.] Windy Gap is Late Cretaceous age. Middle Park is Late Cretaceous and Paleocene.
Source: GNU records (USGS DDS-6; Denver GNULEX).


Publication:
Izett, G.A., 1966, Tertiary extrusive rocks in Middle Park, 
   Grand County, Colorado, IN Geological Survey research 1966: 
   U.S. Geological Survey Professional Paper, 550-B, p. 
   B42-B46.
Usage in Publication:
Middle Park Formation*

Modifications: Geologic Province: Dominant Lithology:
 Revised
 North Park basin
 

Summary:
Locally overlain by upper part of Rabbit Ears Volcanics (new name), and locally overlain by Pete Gulch Member (new name), the lower member of Rabbit Ears Volcanics in Hot Sulphur Spring quad, Grand Co, CO in North Park basin. Is of Late Cretaceous and early Tertiary age.
Source: GNU records (USGS DDS-6; Denver GNULEX).


Publication:
Izett, G.A., 1968, Geology of the Hot Sulphur Springs quadrangle, 
   Grand County, Colorado: U.S. Geological Survey Professional 
   Paper, 586, 79  p.
Usage in Publication:
Middle Park Formation*

Modifications: Geologic Province: Dominant Lithology:
 Age modified
 Overview
 North Park basin
 

Summary:
Is a coarse intermontane fill deposit (mostly lenticular arkosic sandstone and grit) that resulted from erosion of Front and Park Ranges. Laid down in southern part of a large north-trending structural depression known as the North-Middle Park basin [North Park basin]. Rests discordantly on rocks of Pierre or older Mesozoic or Precambrian age. Is older than Rabbit Ears Volcanics. Windy Gap Volcanic Member present locally at base. Upper part divisible into four map units (geologic map). Section 6,600 ft thick measured along Colorado State Hwy 125 northwest from Gold Run that includes Windy Gap (650 ft thick greenish-gray volcanic breccia) and an upper part (5,900 ft thick, very fine, fine- to coarse-grained, arkosic, micaceous sandstone that varies from thin to thick bedded, and olive-gray and dusky yellow, stuctureless, thin-bedded clayey siltstone at base). Late Cretaceous? and Paleocene age (formerly Cretaceous not questioned) assigned on basis of stratigraphic position above Pierre, its fossil leaves, pollen, and spores (listed), and its correlation with Denver Formation.
Source: GNU records (USGS DDS-6; Denver GNULEX).


Publication:
Hail, W.J., 1968, Geology of southwestern North Park and vicinity, 
   Colorado: U.S. Geological Survey Bulletin, 1257, 119 p., 
   (incl. geologic map, scale 1:24,000) [http://ngmdb.usgs.gov/
   Prodesc/proddesc_21345.htm]
Usage in Publication:
Middle Park Member*

Modifications: Geologic Province: Dominant Lithology:
 Revised
 North Park basin
 

Summary:
Reduced in stratigraphic rank in map area from Middle Park Formation to Middle Park Member, basal member of Coalmont Formation. Ranges between 0 and 600 ft thick. Distinguished on basis of its volcanic pebble beds. Consists of arkosic sandstone and conglomerate, sandy claystone, mudstone, and sparse thin carbonaceous shale. The coarser arkosic beds contain angular fragments of quartz, feldspar. The volcanic fragments are mostly medium- to light-gray-weathering porphyritic andesite of pebble (2 in) to sand size. Conglomerate beds are resistant and form steep scarps. Overlies sandstone member of Pierre Shale unconformably. Underlies middle member of Coalmont. Upper contact placed at highest occurrence of gravelly beds with water-worn pebbles of porphyritic andesite. Otherwise the lithologies of the Middle Park and the middle member are similar. Mapped (geologic map) in Grand Co around west and south sides of Ryder Lakes. Is probably a channel deposit derived from a southeast source. Assigned a Paleocene age.
Source: GNU records (USGS DDS-6; Denver GNULEX).


Publication:
Taylor, R.B., 1975, Geologic map of the Bottle Pass quadrangle, 
   Grand County, Colorado: U.S. Geological Survey Geologic 
   Quadrangle Map, GQ-1224, 1 sheet, scale 1:24,000
Usage in Publication:
Middle Park Formation*

Modifications: Geologic Province: Dominant Lithology:
 Overview
 North Park basin
 

Summary:
Is Paleocene and Upper Cretaceous(?) formation mapped mostly in northwest part of quadrangle in Grand Co., CO (North Park basin). Unconformably overlies Pierre Shale (Upper Cretaceous) and older bedrock units. Unconformably overlain by Troublesome Formation (Miocene) and Quaternary deposits. Map unit described as interbedded siltstone, mudstone, sandstone, and conglomerate; dominantly arkosic and micaceous; beds are variegated shades of gray, brown, maroon, and rusty orange; coarse clastics are chiefly derived from Precambrian rocks, primarily granodiorite, quartz monzonite, pegmatite, aplite, and other intrusive rocks, and feldspathic gneiss; in lower 500 ft amount of porphyritic andesite, trachyandesite, and other porphyries increases, locally forming as much as half of the rock. Potentially unstable even on gentle slopes; many landslides. Maximum thickness more than 2,000 ft. Windy Gap Volcanic Member (Upper Cretaceous?) mapped separately at base.
Source: GNU records (USGS DDS-6; Denver GNULEX).