deposits At this time, the best documented occurrences of unfossilized buried upright trees occur within the historic and late-Holocene volcanic deposits of Mount St. Helens (Skamania County, Washington) and of Mount Pinatubo in the Philippines. At Mount St. Helens, both unfossilized and partially fossilized trees have occurred in many outcrops of volcanic debris and mud flows (lahars) and pyroclastic flow deposits, which date from 1885 to over 30,000 BP., along the South Toutle and other rivers. Late Holocene forests of upright trees also occur within the volcanic deposits of other Cascade Range volcanoes. In the space of a few years after the eruption of Mount Pinatubo in 1991, the erosion of loose pyroclastic deposits covering the slopes of the mountain generated a series of volcanic lahars, which ultimately buried large parts of the countryside along major streams draining these slopes beneath several meters of volcanic sediments. The repeated deposition of sediments by volcanic lahars and by sediment-filled rivers not only created innumerable polystrate trees, but also "polystrate" telephone-poles, churches, and houses, over a period a few years. The volcanic deposits enclosing modern upright trees are often virtually identical in their sedimentary structures, external and internal layering, texture, buried soils, and other general character to the volcanic deposits containing the Yellowstone buried forests. As in case of modern forests buried by lahars, the individual buried forests of the Yellowstone Petrified Forest and the layers containing them are very limited in their areal extent. Deltaic deposits Within excavations for Interstate Highway 10 in the United States of America, and in borrow pits, in landfills, and archaeological surveys, unfossilized upright trees have been found buried within late Holocene, even historic, fluvial and deltaic sediments underlying the surface of the Mississippi River Delta and the Atchafalaya Basin of Louisiana. In one case, borrow pits dug in the natural levees of Bayou Teche near Patterson, Louisiana, have exposed completely buried, 4 to 6 feet (1.2 to 1.8 meters) high, upright trunks of cypress trees. Northeast of Donaldsonville, Louisiana, a borrow pit excavated for fill used to maintain nearby artificial levees, exposed three levels of rooted upright tree trunks stacked on top of each other lying completely buried beneath the surface of Point Houmas, a patch of floodplain lying within a meander loop of the current course of the Mississippi River. While searching for buried archaeological sites, archaeologists excavated a 12 ft (3.6 meter) high upright