Suplee-Izee Area

Most of the area between Suplee and Izee in east-central Oregon consists of Cretaceous rocks, but capping many buttes and in isolated outcrops throughout the region are erosional remnants of peralkaline welded tuff, lapilli tuff and tuff breccia (Dickinson and Vigrass, 1965, Plate 1). It is typically 12-15 m thick but may attain 30 m. The rock contains crystal fragments of sanidine, quartz and oligoclase-andesine with rare aegirine, and blue sodic amphiboles including riebeckite and a paler-coloured variety, in a matrix of glass shards which may be devitrified.