shows the Spidel basin lying on the western limb of the Bull 

 Mountains structural basin, iimnediately underlain by the Lance 

 Formation, with Bearpaw Shale and Judith River Formation to the 

 west and Fort Union Formation to the east. The basin itself is 

 mapped as an extensive area underlain by lacustrine (or paludal??) 

 deposits. 



Page 7 includes an interesting discussion of the Lake Basin and 

 Comanche Lake structural impoundments but does not discuss the 

 Spidel basin. Page 40-41 includes water chemistry from a number 

 of Lance Formation wells but none from the immediate township. 



The report is organized with hydrogeologic descriptions by 

 township. The inventory for T5N R23E includes one well completed 

 in section 28, completed somewhere between 75 and 116 feet, and one 

 dug well in section 30, both considered to be finished in the 

 Lance, both yielding adequate domestic supply. No records of water 

 levels are included. 



Swagp Gulcn 



Bibliographic source: Geoindex latlong search 



Author: Whipple, J.W., M.R. Mudge and R.L. Earhart 



Title: Geologic map of the Rogers Pass area, Lewis and Clark 

 County, Montana. 



Series: U.S. Geological Survey Miscellaneous Investigations Series 

 Map 1-1642 



Date: 1987 



Detailed bedrock geologic mapping at 1:48,000 scale shows Swamp 

 Gulch itself underlain by the dominantly clastic Spokane Formation 

 and the transitional Empire Formation (Proterozoic Y), with none 

 of the dominantly calcareous and dolomitic Helena Formation within 

 the watershed. The outcrops at the mouth of the drainage are mapped 

 as Proterozoic Z intrusives (diorite). A portion of the Mike Horse 

 Stock (Paleocene/Eocene monzonite porphyry or quartz monzonite 

 porphyry) . 



Upgradient contributing drainages (Pass Creek, Anaconda Creek, 

 etc.) are underlain by the same lithologies, with the addition of 

 small areas of Helena Formation at higher elevations along the 

 divides. 



Structurally within the Hoadley Thrust Plate, one of a series of 

 stacked thrust plates shown on the map area. Dips shown are low 



61 



