Pyroclastic rocks associated with the Taylor Creek Rhyolite, Scales Canyon

Pyroclastic deposits formed during the emplacement of the 28.6 my old Taylor Creek Rhyolite are exposed in a 2 km long section in Scales Canyon. As much as 50 m of pyroclastic fall, surge, and flow deposits as well as eolian sandstone have been recognized in five measured sections. Three eruptive sequences are proposed: I — a lower, predominantly pyroclastic flow and surge sequence; II — a middle pyroclastic fall sequence; and III — an upper sequence of two coarse pyroclastic breccias. Paleomagnetic measurements on clasts from the two units within sequence III indicate the lower unit was emplaced as a hot (>500°C) pyroclastic flow, whereas the upper unit was emplaced as a mixture of hot (>500°C) and cold (<300°C) clasts. Both units apparently represent dome-collapse breccias. The lower unit contains only hot material from the interior of the dome, whereas the upper unit also contains a component of the cooler dome carapace.

The Scales Canyon pyroclastic deposits were apparently erupted over a short span of time from two or more nearby dome-related vents. Individual vents cannot be identified because the deposits are mineralogically similar.