First use of the Sixty Mile [Sixtymile] Formation of the Chuar Group. Age is late Precambrian.

Source: GNU records (USGS DDS-6; Menlo GNULEX).

Named as the upper formation of the Chuar Group for its type section in Sixty Mile Canyon, west side Colorado River, Coconino Co, AZ in the Southern Rocky Mountain region. Outcrops found on north side of upper part of canyon. Makes up the topmost 120 ft of Nankoweap Butte where it unconformably overlies the Walcott Member (new) of the Kwagunt Formation (new) of the Chuar and unconformably underlies Tapeats Sandstone. Was previously assigned to Tapeats Sandstone, the Chuar terrane, and other informal terms. Base of formation is placed at base of silicified breccia beds that rest on the eroded surface of shale of the Walcott. Clasts in the breccia were derived from the Walcott. Breccia varies from 20 to 50 ft thick. Above the breccia is a fine-grained, red, generally flat-bedded sandstone with frequent 1 ft thick lenses of breccia, and a 20 ft thick layer of breccia is present above the sandstone. Easy to confuse sediments of Tapeats Sandstone, the next younger unit with the Sixty Mile. Is probably of fluvial origin. Of late Precambrian age. Columnar sections. Geologic map; shown only near Sixty Mile Canyon.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Upper formation of Chuar Group of Grand Canyon Supergroup. Spelling [geographic part of name] revised from Sixty Mile to Sixtymile to agree with spelling of canyon on Vishnu Temple quad. Type section measured in north fork Sixtymile Canyon 36 deg 12' 42" N, 111 deg 50' 45" W, Coconino Co, AZ, Southern Rocky Mountain region where Sixtymile 57-64 m thick. Overlies Kwagunt Formation of Chuar. Unconformably underlies Tapeats Sandstone. Lower member of purple, red and pink beds of (in sequence): 1) quartzose, very fine grained, hematitic laminated sandstone; 2) thin-bedded, micaceous, fine to very fine grained sandstone; 3) monomict and polymict breccia; 4) crudely bedded, fine- to coarse-grained, poorly sorted sandstone with grains angular to subrounded; 5) monomict and polymict breccia; 6) finely laminated to very thin bedded, soft, sandy siltstone. Middle member red to pink, very fine grained to silt sized quartzite. Upper member has sandstone facies in southwest axis syncline of red and brown, fluvial, cross-bedded sandstone with white chert fragments, and conglomerate facies fine to coarse grained with angular to subangular granule-, pebble-, and scattered boulder-size fragments. Cross sections; columnar section; geologic map. Deposited in deepening trough of north-trending Chuar syncline as a result of regional uplift, tilting, and faulting. Of continental origin. Correlated with Windermere. Is about 830 m.y. and younger.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Retained in the Proterozoic Grand Canyon Supergroup but removed from the Chuar Group because of its lithology (very fine to coarse grained landslides and breccia-bearing red beds of continental origin) which contrast with the dark-gray marine shale of the underlying Kwagunt and Galeros Formations of the Chuar. Deposition was continuous across the Kwagunt-Sixtymile Formation boundary; a 10-cm thick transition zone records a time of marine emergence. Section at Nankoweap Butte which differs in some details from Sixtymile Canyon (Elston, 1979). Sixtymile at the butte conformably and gradationally overlies Kwagunt Formation. The transition zone at the butte contains a layer of unreworked airfall tuff at base. The zone is overlain by very fine grained red laminated sandstone belonging to the Sixtymile. Sandstone of the lower member of the Sixtymile was folded, eroded, and followed by deposition of breccia-bearing sandstone and landslides. The landslides consist of chaotic polymict breccia derived from Chuar rocks. Breccia layers occur in all three members; the lower two in the lower member show no evidence of reworking; the two breccias in the middle member show the effect of transportation and sorting; the breccia at the base of the upper member is unreworked and unsorted. Cross sections; columnar sections. Report area lies in the Southern Rocky Mountain region.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Is the uppermost unit in the Grand Canyon Supergroup. Unconformably overlies Tanner Member of Kwagunt Formation of Chuar Group. Unconformably (called the "great unconformity) underlies the Tapeats Sandstone. Is 59 to 64+ m thick. Divided into lower, middle, and upper members which are separated from each other by unconformities. Age is Late Proterozoic. Represents interval from slightly older than 825 Ma to about 570 Ma. Sixtymile pole has a westerly position, probably representing a shift form Nankoweap and Chuar time. The pole indicates correlation of underlying Chuar with part of the Mackenzie Mountains Supergroup. A sill in the Tsezotene Formation of the Mackenzie Mountains Supergroup dated at 770 Ma has a pole identical with Sixtymile pole. Is in the Southern Rocky Mountain region of northern AZ.

Source: GNU records (USGS DDS-6; Denver GNULEX).