The Aldercrest-Banyon landslide was a major slow-moving landslide in the east Kelso, Washington neighborhood of Aldercrest beginning in early 1998 through 1999. The disaster ended up being one of the worst urban landslides in United States history in terms of cost. The landslide is one of the most notable in Washington state, which has many landslides due to its mountainous terrain. The Aldercrest-Banyon landslide was the first landslide disaster in the United States that the Federal Emergency Management Agency (FEMA) declared an official disaster area. History The Aldercrest residential neighborhood was completed in three phases between 1973 and 1979. It is built on an ancient landslide that may have occurred during the Missoula floods (15,300–12,700 years ago). Approximately 2 to 14 million years ago, the Columbia River deposited gravels, sands, silts, and clays and are known as the Troutdale Formation. In the area of the landslide, along a northwest-southeast trending ridge about one-half mile east of Interstate 5, the Troutdale Formation ranges from approximately thick in the Kelso area and was deposited upon a much older, near-shore marine sedimentary deposit known as the Cowlitz Formation. These areas are known for landslide activity. At the base of the slope is the Coweeman River. The landslide Following 3.5 years of above average rainfall the water loosened layers of clay but did not percolate through, and the load on the earth was increased. The Troutdale and Cowlitz formations began to slip. Also a road excavation in February 1998 across the lower part of the slide may have been a trigger to cause the initial reactivated movement, which then caused storm drains to break and storm water to be fed back into the slide. Logging operations at the toe of the landslide may also have contributed to the reactivation. Aldercrest-Banyon residents began to see signs of ground movement. In February 1998 underground utilities began to break from the pressure and once broken storm drains fed abundant water into the system, it further increased the earth movement rates. By March homes began to show signs of movement and stress. These included jammed doors and windows, and concrete foundations cracking. Other signs were separation of chimneys from foundations, drywall bulging over nailheads, twisted ceiling beams, water flowing through foundation cracks, bulging walls, kitchen cabinets separating from the walls and creaking, popping and snapping noises could be heard in the homes. In mid-April 1998, a high crack