We began our three week northern Arizona and southern Utah National Park tour today. First stop, Petrified Forest National Park, which includes a portion the Painted Desert. Last year you got a history lesson, this year you are going to get a geology lesson.
The petrified wood in this area was formed 225 million years ago. The Colorado Plateau area of northeastern Arizona was located near the equator and on the southwestern edge of the landmass known as “Pangaea”. (Eventually this super-continent separated to create our current continents). The lush rain forest had huge trees that over time, died or were knocked over. Some logs were buried by sediment before they could decompose. Volcanoes to the west spewed tons of ash into the atmosphere and winds carried the ash into the area where it was incorporated into the deepening layers of sediment. Ground water dissolved silica from the volcanic ash and carried it through the logs. This solution filled, or replaced cell walls, crystallizing as the mineral quartz. Iron rich minerals combined with quartz during the petrification process, creating the brilliant rainbow of colors. The result is absolutely beautiful.
The painted desert is composed of stratified layers of easily erodible siltstone, mudstone and shale. These fine grained rock layers contain abundant iron and manganese compounds which provide the pigments for the various colors. The erosion of these layers has resulted in the formation of the badlands (dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded by wind and water) topography of the region.
The park also has ruins and petroglyphs from the people that in inhabited the area about 2,000 years ago. The picture below is of Newspaper Rock.