The volcano is 20 miles in diameter, has an approximate volume of 80 cubic miles, and it possesses a large oval-shaped caldera four by five miles in diameter, called the Newberry Caldera. Within the caldera there are two lakes (Paulina Lake and East Lake), many cinder cones, lava flows, and obsidian domes.
A deep gash in the northern caldera wall, The Fissure, is the end of a 29-mile long series of fractures called the Northwest Rift Zone. Approximately 6100 years ago fissure basalt flows erupted from the rift and covered part of Newberry's northwest flank.
A great deal of volcanic activity has occurred on Newberry's shield, which itself has one of the largest collections of cinder cones, domes, lava flows, and fissures in the world (local residents call these parasitic vents the "Paulina Mountains" as if they were their own mountain range). Most of the cinder cones are 200 to 400 feet high and have shallow saucer-shaped summit craters. They are typically surrounded by basalt or andesite that erupted from their bases, forming large lava beds. There are also about 20 rhyolite domes or fissures on the eastern, southern, and western flanks. Larger examples include; McKay Butte on the west flank (580,000 years old), China Hat 780,000 years old) and East Butte (850,000 years old) on the far eastern base.
All these various volcanic features are between several hundred thousand years to around 6100 years old and most lie in one of three broad zones on the shield. The oldest zone is on the eastern part of the shield and is apparently a more recent analog of the basaltic volcanism that formed central Oregon's lava plateau. Another zone is on the northwestern part of the shield and consists of vents that parallel a series of faults near the base of the shield (see Northwest Rift Zone). The latest basaltic eruptions on the volcano occurred here around six thousand years ago. On the southwestern part of the shield is the third major volcanic volcanic zone. The vents there parallel the Walker Rim fault zone. Additional vents not in any major volcanic zone run parallel to the caldera rim and may be associated with caldera fractures.
Newberry's highest point is located 1500 feet above the southern caldera floor on Paulina Peak, which is just one peak on the caldera rim. The volcano's south flank descends into the basaltic flatlands of central Oregon.
During the Apollo program parts of the volcano that resembled the Moon's surface were used to train astronauts.
See also: Newberry National Volcanic Monument
Geology
Newberry Caldera has existed possibly as long as 500,000 years when the cone of the volcano is thought to have first collapsed. Subsequent caldera-forming collapse events have further deepened the caldera but volcanic material and lakebed sediments have largely filled in much of this depth (see Newberry Caldera for details).