In the writer’s estimation the Knerr Ranch “Slate” (informal name initiated herein, for the rock is not a true slate, but is slaty to the degree that it forms an excellent platy rock) is the most valuable dimension stone within normal economic haul limits of Missoula. The Knerr Ranch holdings lie on Highway 28, about 3.0 mi (4.8 km) north of the Clark Fork River bridge at Perma, a highway distance of about 185 km (115 mi) to Missoula.
Rancher Ms. Joyce Knerr has recently allowed a royalty-based highwall extraction of interbedded slaty argillite and fine-grained, slaty quartzite exposed within 50 m (164 ft) of the highway, at the nose of a N-S striking foliation ridge. This rock belongs to the lower portion of the Proterozoic Lower Pritchard Formation of Harrison, et al., 1986. Lower Pritchard beds are of seven distinct lithologies. At the quarry, vertical beds are ripped by a toothed backhoe bucket and hand-sorted onto strapped pallets, by the Native Rock Design Company, of Missoula. Judging from spoil, only about 30 percent of the ripped rock is recovered for sale.