In the Sun River area of Montana ruminants have established licks in only 3 of 25 outcropping bedrock units, which locally are mantled by glacial till. The 3 units are all mudstones deposited in relatively shallow-water marine environments. Rapid chemical and spectrographic analyses of the rock and of the spring water in the licks were compared with analyses of rocks and waters unrelated to licks. Sodium bicarbonate and sodium sulphate are the only compounds that occur in much greater quantities in the licks than elsewhere. Boron and lithium also occur in slightly larger quantities in the licks. Calcium, magnesium, and strontium are generally present in lesser quantities. Chlorine occurs in small but normal quantities in both the lick and nonlick waters. Big game animals, predominantly elk (Cervus canadensis) are commonly observed at the licks, especially during the spring and fall. The licks appear to be used socially as gathering places as well as for their mineral content.