Further south, near Mount St. Helens, is a similar situation, where the St. Helens Fault Zone (SHZ) is believed to be the eastern edge of the Crescent Formation, but the pre-Cenozoic continental basement is near Mount Rainier. Separating these is the marine sedimentary formation known as the Southern Washington Cascades Conductor (SWCC); it is possible that it was deposited over a fragment of Siletzia. Or not: the oldest parts of the SWCC likely predate Siletzia, and the nature and location of the contact between these two formations is unknown.