The Fifes Peaks Formation is a volcanic rock unit in the Mount Rainier and central Washington Cascades region that preserves an important record of early Cascade volcanism. Formed during the late Oligocene to early Miocene, its rocks date to roughly 20 to 27 million years ago. It consists mainly of vesicular basaltic-andesite and andesitic lava flows with volcanic breccias, and in some places overlies the older Ohanapecosh Formation. The formation includes the informal Sun Top unit in the White River area and also contains a silicified rhyolite tuff from the Clear West Peak volcanic center. Its thick porphyritic flows, columnar jointing, and varied breccias reflect diverse volcanic processes.