These are the highly altered volcanic rocks of an island arc that have been accreted against North America at the end of the Paleozoic. The rocks are green because of chlorite alteration during the circulation hydrothermal waters near the volcano. The rocks are Cambrian, the same age as the slates and distal rocks thrust up during the Antler Orogeny…but these are tough to work in…they are a geochemist’s nightmare. Hats off to those who can do this work! Image courtesy of Professor Burchfiel.