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Thursday, July 29, 2004 - Page updated at 12:00 A.M.
Ginkgo Petrified Forest: Tread with wonder in ancient path of lava
By Cathy McDonald
The inhabitant of the stone enclosure set into the sagebrush and balsam-root-covered hill in front of me hadn't been so fortunate. Visible through the locked gate was the preserved remnant of a ginkgo tree. Protected against vandalism, the tombs of 21 other petrified logs of various species dot the hillside trails of Ginkgo Petrified Forest State Park near Vantage.
The park, a National Natural Landmark, contains one of the most unusual petrified forests in the world. The tissue structure of the tree specimens is so well-preserved that dozens of individual species have been identified. The site is remarkable not only because of its wide variety of preserved trees, but because they are preserved in lava. People come from all over the world to visit the park.
"We've had some visitors who practically get off the plane in Seattle and come straight here," said Joyce Nelson, an interpretive assistant at the park. "There's been people from literally every continent we had workers here who had done construction in Antarctica."
View of history
From my wind-whipped viewpoint on the hill, I tried to imagine the scene 15.5 million years ago. According to a report by Jack Powell, a retired geologist from the Washington Department of Natural Resources, by that time huge amounts of lava had already erupted, and the lava beds here were more than a mile thick.
A pumice layer beneath the petrified trees indicates that a volcano erupted to the west, producing mudflows that transported downed trees into the lake. These tree-laden lahars were probably similar to those of the 1980 Mount St. Helens eruption, but they happened on a larger scale and took place over greater periods of time.
A variation on the theory proposes that normal rivers and flooding (not mudflows) carried the wide variety of trees from different elevations down to the lake.
When the basalt flows resumed erupting from the southeast, the Ginkgo Flow poured into ancient Lake Vantage, now full of a jumble of tree trunks brought down by the mudflows. The flows cooled as they hit the lake, so when the lava covered the water-soaked logs, the trees did not burn. Over time, silica-rich groundwater gradually replaced the woody material with minerals.
During the end of the last Ice Age (15,500 to 13,500 years ago), a series of ice dams in northern Montana trapped huge lakes of glacial meltwater. When the dams failed, huge floods repeatedly swept over eastern Washington. During one flood, waters 1,200 feet deep swept over portions of Ginkgo Petrified Forest State Park. These floods eroded the land within the park, exposing the petrified logs preserved in basalt.
Two miles to the east, the park's interpretive center perches high above the dammed Columbia River, here called the Wanapum Reservoir. Outside, petrified logs scattered around the building make for unique landscaping.
Inside the center, dozens of cut-and-polished cross-sections of petrified wood glisten in cases, identified by species. Actually, out of the thousands of trees discovered here, only a handful were ginkgo, but the rarity of petrified ginkgo wood, found only in a few places in the world, gave the park its name.
Workers uncovered petrified logs in 1927 while constructing roads in the area. Local Native Americans had used the material for arrowheads and other tools for possibly thousands of years; some of these artifacts are displayed in the center and at the nearby rock shop. In 1931, George F. Beck, a professor at what is now Central Washington University, researched the site and lobbied for its preservation. Workers with the Civilian Conservation Corp (CCC) created the trails, unearthed the trees and built the oldest part of the interpretive center during the 1930s.
Outside the visitor center is an unexpected bonus. Native American petroglyphs, carefully removed from cliffs farther up the river before the dams were built in the 1950s, are set into the building's foundation. The rock carvings are considered one of the best examples of petroglyphs in the region.
Cathy McDonald is a freelance writer who lives in Renton.
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