Complex sentence: The Flatside Wilderness is dominated by the Pennsylvanian Jackfork Sandstone, which is a massive-bedded, fine-grained, brown, tan, or gray quartzitic sandstone.
Split into simpler sentences: The Flatside Wilderness is dominated by the Pennsylvanian Jackfork Sandstone. The Jackfork Sandstone of the Flatside Wilderness is massive-bedded, fine-grained, brown, tan, or gray quartzitic sandstone.