Emery — Green River Desert Section, Utah. 553 



assigned to the Lower Triassic), constituted principally 

 of red-brown sandstone and shale, but containing at its 

 base a prominent zone of buff shale and sandstone. The 

 Moenkopi is unconformably overlain by the Shinarump 

 conglomerate (Triassic), which is a very valuable key 

 formation for correlation purposes, because of its pecu- 

 liar lithologic character and widespread distribution. 

 The variegated shales of the Chinle formation (Triassic) 

 which lie perhaps unconformably above the Shinarump, 

 are succeeded, also perhaps unconformably, by the mas- 

 sive, much cross-bedded sandstones of the Wingate 

 (Jurassic). There is some evidence to indicate that 

 the overlying beds, here tentatively correlated with the 

 Todilto formation (Jurassic), rest unconformably on the 

 Wingate. The Todilto (?) in addition to a rather hetero- 

 geneous mass of reddish shale and dirty gypsum, con- 

 tains near its base a dense limestone which is fossil- 

 iferous and is therefore an invaluable key bed, as it occurs 

 in the midst of a considerable thickness of unf ossilif erous 

 strata. The Navajo sandstone (Jurassic) succeeds the 

 Todilto (?) and is composed of massive red sandstone at 

 the base, with thinner-bedded red sandstone and sandy 

 shale above and a prominent thick belt of gypsum at the 

 top. The Wingate, Todilto (?), and Navajo together 

 form what has been called the La Plata groups of rocks. 

 The McElmo formation (Cretaceous?) comes next above 

 the Navajo and consists of coarse white sandstone and 

 conglomerate at the base (the Salt Wash sandstone mem- 

 ber), variegated shales containing dinosaur bones and 

 well polished pebbles resembling gastroliths in the mid- 

 dle portion, and at the top, coarse sandstones and con- 

 glomerates with minor quantities of variegated shale. 

 The McElmo is believed to rest unconformably on the 

 Navajo. An unconformity occurs also at the top of the 

 McElmo, for it is in places overlain by a thin bed of 

 Dakota sandstone (Upper Cretaceous) but is elsewhere 

 in contact with the Mancos shale (Upper Cretaceous). 

 This shale, "which is several thousand feet thick, is blue- 

 gray to drab in color and f ossilif erous at numerous hori- 

 zons. It is an important stratigraphic marker because of 

 its lithologic character and fossil content. 



The areal distribution of these formations in the 

 Green River Desert is shown in the geologic sketch map 



