Geologic mapping at 1:62,500 emphasizing surficial geology and 

 glacial features. Sampling site is shown very near the contact of 

 alluvium/colluvium material filling the preglacial Missouri channel 

 and "ground moraine". Ground moraine in the quad is described as 

 compact and of low permeability. The till is shown as 60 feet 

 thick near Big Sandy. 



Nearby wells shown, indicating the fill within the channel is on 

 the order of 100 feet thick. Stratigraphic relationship between 

 the till and the alluvium/colluvium is unclear from the map. 



Bedrock formations underlying the surficial deposits are the Upper 

 Cretaceous Clagget Shale (sandy in the upper 150 feet) and the 

 overlying Judith River Formation. The immediate area of the site 

 is underlain by the Claggett. 



The map includes a qualitative summary of the engineering 

 characteristics of the map units. Permeabilities of the 

 undifferentiated alluvium/colluvium are described as highly 

 variable. Permeability of the till and Claggett are very low. 

 The site is near the edge of the sheet, so the distribution of map 

 units in most of the upgradient Big Sandy Creek basin is not shown, 

 although Cretaceous bedrock units must dominate the basin. 



Bibliographic source: Geoindex lat-long search 



Author : Swenson , F . A . 



Title: Geology and ground-water resources of the lower Marias 

 irrigation project, Montana. 



Series: USGS Water-Supply Paper 1460-B 



Date: 1957 



Geologic mapping at a scale of 1:94500 emphasizes surficial 

 geology. The general area of the site is mapped as paludal, 

 described as plastic clay and silt. This map unit covers several 

 sections in this part of the pre-glacial Missouri channel. The 

 valley margin, possibly underlying the site, is mapped as a kame 

 terrace with unclear(?) stratigraphic relationship to the paludal 

 silts. 



Isopach map included in the text shows the total thickness of 

 unconsolidated deposits exceeding 200 feet near Boxelder, without 

 coverage of Big Sandy. Interesting observations about the 

 retention and infiltration of water entering the Lonesome Lake 

 Basin. Page 51 includes table showing 6 years of monthly discharge 

 data from Big Sandy Creek 2.5 miles SE of Big Sandy (pre-irrigation 

 project - did the irrigation intended ever happen??). 



