What type of rock has a high ability to absorb moisture?  Answer the above question based on the context below:  Big Butte Creek drains approximately 245 square miles (635 km2) of southern Oregon. Elevations range from 1,562 feet (476.1 m) at the creek's mouth to 9,495 feet (2,894 m) at the summit of Mount McLoughlin, with an average of 3,528 feet (1,075 m). About 56 percent is federally owned by the Bureau of Land Management and the United States Forest Service, 44 percent is privately owned, and a small fraction belongs to the City of Medford.The Big Butte Creek watershed experiences a Mediterranean climate. Temperatures range from 10 °F (−12 °C) in the winter to 100 °F (38 °C) in the summer. Precipitation averages between 35 and 80 inches (890 and 2,000 mm) annually. Most precipitation occurs between November and March. Nine percent of the watershed's surface runoff is collected from rain, 35 percent from rain on snow, and 56 percent from snow. The watershed contains the largest groundwater source in the entire Rogue River basin; one major outlet is at Big Butte Springs.The watershed is split into two geographic regions: the High Cascades and the Western Cascades, both volcanic in origin. The Western Cascades compose the western two thirds of the watershed. This region is highly eroded, being between 17 and 38 million years old. Its unstable slopes are primarily made of pyroclastic rock. Due to the rock's high ability to absorb moisture, earthflows are common. The High Cascades are much younger, around three to seven million years old. Mount McLoughlin is the most prominent High Cascade volcano in the watershed, last erupting between 20,000 and 15,000 years ago. Basalt and andesite are the most common rock types in this region.Nearby watersheds include Little Butte Creek to the south, small Klamath River tributaries such as Fourmile Creek to the east, the South Fork Rogue River to the east and north, and minor tributaries of the Rogue River including Reese and Indian creeks to the west.
Answer:
pyroclastic