Siletzia is a geologic terrane that is currently part of the North American continent, but it is believed to have originated as an oceanic plateau that was formed at a spreading center in the Pacific Ocean. The exact location of this spreading center is not known for certain, but one hypothesis suggests that it may have been located near present-day Bremerton, Washington.

This hypothesis is based on the presence of certain types of rocks in Siletzia that are typically associated with oceanic spreading centers, such as seafloor basalts and volcanic ash deposits. These rocks are similar to those found in other oceanic plateaus, such as the Ontong Java Plateau and the Manihiki Plateau.

In addition, the age of the rocks in Siletzia is consistent with the timing of seafloor spreading in the Pacific Ocean. The oldest rocks in Siletzia are about 170 million years old, which corresponds to the time when the Farallon Plate was spreading away from the North American Plate.

If Siletzia did originate near Bremerton, it would mean that this region was once part of the Pacific Ocean and that it has since been accreted onto the North American continent. This would be an important piece of information for understanding the geologic history of the region and the evolution of the Pacific Ocean basin.