Exposed within the interior of these tracks are a variety of intrusive and extrusive igneous structures. They include the extensive hydrothermal alteration of rhyolites and gabbros and a central megabreccia created by hydrothermal dissolution and collapse. The siliceous megabreccia is at least 40m thick in its center - to only a few meters thick along its edges. The breccia consists of fragments of white to dark gray cherty material, quartz-rich bass, diagenetic clap nodules, and stromatolitic snares. It is intensively silicified.