PAINTED DESERT MEMBER (Upper Petrified Forest member)  
Updated 1/24/09

The magnificently colored Painted Desert Member of the Petrified Forest Formation rests unconformably on the Sonsela Sandstone. It is composed of a series of grayish red, brown, and reddish purple mudstone, siltstone and sandy siltstone beds with some very large scale crossbeds. The beds are flat and lenticular and generally are more than 50 feet thick, and more than a quarter of a mile long. Some beds show low to very low angle very large scale crossbeds. The units in the painted Desert member are more flat bedded, can be traced farther laterally, and have fewer well-defined channels than units in the Blue Mesa member. In some areas it is over 1000 feet thick, but typically 500 feet thick over most areas. The majority of this unit lies on the north end of the Petrified Forest, and outcrops over a large area north to the border. All of these shots were taken on the Park loop north of I40.

The rose colored bentonites are capped with the basalt portion of the Tertiary Biddahochi formation. The Biddahochi is a large series of lake, fluvial and volcanic deposits extending from the north end of the Park, to the south end of Black Mesa in northern Arizona.

Low lying mudstones and bentonites form badlands extending all the way to the distant horizon where the distant hills are formed of the Owl Rock member of the Chinle Group, a mostly lacustrine deposit containing a molluscan fauna.

White mudstones cap the ruddy bentonites of the Painted Desert member of the Chinle Group north of I40.

Another view of the Painted Desert Member of the Chinle north of I40. The rolling reddish badlands extend as far as the eye can see, the visibility on this day was over 100 miles! This is common in Northern Arizona, where the high altitude air is clear and dry.

This magnificent scene North of I40 shows white mudstones capping the red clays. Of great interest here are the shallow ridges seen on the slopes of the hills. These are slumping structures, and form when the sides of the ridges get wet after a rain, and the whole hillside slides down because the clays are very slick and slimy when wet, and form a bearing surface.

Although petrified wood is less common in the Painted Desert member, there is a virtual Disney Land of sedimentary structures. This aerial view of the deposits north of I40 shows clearly the numerous slumping structures in the red bentonites.

Another aerial view of the Painted Desert member north of I40. Note the flatlands formed between the ridges from erosion of the badlands. The white chalky deposit below is a lacustrine mudstone.

Although there are far less petrified logs in the Painted Desert member, large silicified and permineralized logs do occur. This aerial view shows a log breaking up and fragmenting down a gully from the ridge top. View taken from north of I40 in the Petrified Forest.

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