A comprehensive record search and ground-truth investigation was performed from late summer to early winter of 1976, of federal and state lands within 114 bentonite mining claims under lease by Aurora Metal Company in southwest Valley County, northeastern Montana.21 The leased area, parts of which would be affected by projected bentonite mining activities, comprises 20,400 acres of weathered upland terrain drained by Brazil and Little Beaver Creeks.
Local geology, geomorphology, and geohydrology reveal that the surface of the study area has been intermittently modified by ongoing erosion; natural effects of disturbance have been aggravated by the disruptive effects of livestock grazing, vehicular traffic, road and railroad construction, and exploration for and extraction of bentonite. Also, artifacts were collected from many parts of the surface, and certain of the surficial features were potted by artifact collectors and inquisitive others prior to the inventory. These agencies of disturbance have combined to create a dynamic and vulnerable landscape in which only 43 per¬ cent of the identified cultural heritage sites have escaped degradation.
Three hundred and three separable sites of precontact activity (n= 298) and recent historic activity (n= 3) were inventoried on-the-ground on 102 of the 114 mining claims, between 27 July and 17 August, by a survey team from Montana State University. The inventoried heritage sites represent activities associated with settlement (habita¬ tion), food procurement (bison kill/drives), raw material procurement and tool production, and ceremonial systems. Observed archaeological features include: fire-broken rock; hearths; stone circles; rock clusters; cairns; stone piles; drive lines; rock alignments; and surface depressions. Recovered prehistoric artifacts include: projectile points; knives (bi¬ faces); pieces esquillees; end scrapers; edge-retouched flakes; hammerstones; choppers; a zoomorphic stone effigy; lithic waste; and earthenware ceramics.
The 303 heritage sites were evaluated and assigned significance levels (CRES) in accord with established criteria to determine their relative national importance as cultural resources. Four (1.3%) Level 1 prehistoric sites are sufficiently important to warrant nomination to the National Register of Historic Places; however, only three of these sites are recommended for nomination. Thirty-three (10.9%) sites are significant at Level 2, 146 (48.3%) at Level 3, and 120 (39.5%) at Level 4; certain of these sites merit protection.
The effect of bentonite mining cannot be predicted at 215 (71%) of the heritage sites, since these sites occur at distances greater than one-quarter mile from projected pit locations or because pit locations (on state lands) were not specified by the Company. Indirect detrimental effect is anticipated at 70 (23.1%) sites in the study area, with direct impact is predicted at 18 (5.9%) sites. The indirectly affected sites distribute on 42 mining claims, while the directly affected sites occur on 15 claims; both indirectly and directly affected sites are located on 10 claims.
Avoidance of potentially adverse affects on sites is the preferred action alternative. However, since the practical¬ ity and feasibility of avoidance as an alternative remains a matter for future determination between the Company and public land managers, recommendations specify the most effective mitigation approach as though each projected pit location will be mined as planned. Further action to preserve and protect affected sites is not required at 239 (79%) of the heritage sites. The mapping of surficial features is recommended at 40 sites, mapping augmented by test excavation at 23 sites, and excavation at one site. Recommended mitigation procedures are appropriate to and contingent upon the circumstances presented by anticipated mining actions at specified locations. Since any future changes in pit location will alter the proximity relationship between identified sites and mined locations, such changes may be cause for a reappraisal of proximity, impact, and the advisability of protective action on the part of the Company.