new reservoir came improvements to the Powell Butte park, including resurfaced and realigned trails, reduced environmental impacts, better accessibility measures, and reduction of steep grades. The government also built a visitor center, caretaker's house, public restrooms, maintenance yard, and a permeable parking area that permitted filtration of rainwater through asphalt to an underground stone bed, where it could be absorbed by the soil and then into the nearest aquifer. Built between 1993 and 1998, the Robertson Tunnel runs for through the Tualatin Mountains. Located underground, it is the deepest train station in North America. The tunnel displays a core that exhibits Boring Lava deposits. For the first of the tunnel, the core shows Boring lava flows with cinder, breccia, and loess dated from 1.47 million to 120,000 years ago, which have been deformed by the Sylvan fault. With the Oatfield fault, the Sylvan fault trends to the northwest, extending northwest and southeast of the tunnel. It is of Quaternary age and lacks surface expression, possibly as a result of its extensive burial by loess along its length. In 2000, the nonprofit Friends of Mt. Tabor Park was formed to help maintain the Mount Tabor Park area, located east of downtown Portland. They have an organizational website and publish a bi-annual newsletter called the Tabor Times. Membership requires dues, and they also rely on donations and a gift shop for financial support. In September 2017, the Hogan Butte Nature Park opened in the city of Gresham, encompassing an area of that includes the extinct Boring Lava Field volcano Hogan Butte. This park opened after more than 25 years of processing, supported by a 1990 bond from the city and two regional Metro bonds. Collaborators for opening the park include the U.S. Forest Service, local citizens, Metro, The Trust for Public Land, and the Buttes Conservancy organization. Gresham is one of just a few places in the United States with volcanoes contained in its city limits. Mount Sylvania and Mount Scott lie within the limits of Portland, in the southwestern and southeastern parts of the city, respectively. Geology There are 90 volcanic centers within a radius of Troutdale and more than 32 vents within a radius of Kelly Butte. Mostly small cinder cone vents, these volcanoes also include some larger lava domes from shield volcanoes at Mount Sylvania, Highland Butte, and Larch Mountain. The Boring Lava Field marks the densest volcanic vicinity