sentences:  These Roseburg volcanics were followed by the Siletz River Volcanics in the northern portions of the range, and lastly a series of basalt flows from the Columbia River basalts also added to these formations with some smaller flows in-between.Much of the formations are the result of pillow basalt formations created when a hot basalt flow rapidly cooled upon meeting the salt water of the ocean.These deposits offshore were then pushed into the continental plate as a forearc basin rotating slowly over millions of years.