Mona Butte section 
Fall River formation (in part) Thickness in feet. 
31. Sandstone, medium -grained, cross- 
bedded to cross -laminated, friable, 
weathers ochrous red to orange. 
5. 3 
30. Sandstone, medium-grained, massive, 
ledge-forming, crudely tabular, cross- 
laminated. Weathers variably yellow gray 
or orange-red. Considerable ferruginous 
cement, concretionary layers, and scattered 
small, hollow concretions. Basal 0.1 foot 
is ironstone. 51.0 
dis conformity 
Lakota formation 
29. Siltstone, clayey, gray, weathers to white 
clayey wash. Peppered with ferruginous 
specks from weathering of spherulites of 
siderite. Becomes sandy at base. 4.7' 
28. Sandstone, fine-grained, massive, upper 
0. 5 to 1.0 locally quartzitic. Light gray 
to yellowish gray. Locally has vertical 
tubular ferruginous concretions. 
2. 7 1 
