The Tertiary

Payson Basin Formation


(Uploaded 9/27/09)

The Payson Basin is a basin fill and lacustrine deposit located about 15 miles south of Payson along Rye Creek. The deposits are about 15 miles by 10 miles in extent, and are nestled between the Sierra Ancha and Mazatzal mountains, and represents a lowland area filled with conglomerates, siltstones, sandstones and freshwater limestones. It is part of a series of Pliocene through Pleistocene basins extending along a northwest to southeast line that includes the Tonto Basin, Verde Basin, and San Carlos Basins on the south end. The formations contained in the basins lie unconformably on igneous, metamorphic and siliclastic sedimentary rocks of the region.

Deposits of the Payson Basin can be easily seen along Highway 89 on either side of the turn off to Roosevelt lake in the roadcuts and along the sides of the road as light colored limestone, and siltstones. Although fossils are few along the highway, other areas of the basin have produced Pliocene Pliohippus horse teeth, plant hash such as reed and aquatic plant impressions, worm burrows and small turriculate form gastropods. Taylor in his report on Blancan mollusks in the western United States mentions identifies the gastropod species as Lymnaea, Promenetus, and Physa. Pollen analysis of the sediments found in the Basin indicate that the Pliocene climate was a woodland-savanna community, dominated by pine.

In the Payson Basin the lacustrine sediments include a fairly high proportion of sand and pebbles. Some of the beds are buff to light rusty red, but the prevailing colors are light creamy yellow to white, similar to the beds in the Verde and San Carlos Basins.

Six mappable units are recognized within the Payson Basin according to Pedersen: Undifferentiated bedrock, Older alluvium, Fine grained alluvium, Coarse grained basin fill alluvium, Terrace alluviums, and Floodplain alluvium. Below you will find images of our exploration of the Payson Basin.


Typical scene in the Payson basin. The Mazatzals mountains are in the distance, and in the foreground the lowlands contain alluvium, shales, sandstones, and limestones of the Payson Basin formation. The butte off to the right is Table Mountain, which has a sandstone cap from the Payson Basin formation. This view from near Rye.

Parked along the road in Rye, the white limestones of the Payson Basin formation cover the road in roadcuts. Some are highly fossiliferous, and contain abundant gastropod fauna. Also found at this site, were ostracods, plant hash, and mummified roots.


This piece of white dolomite, contains hundreds of small coiled gastropods, all of one species. All of the freshwater gastropods found in the Payson basin are usually under a quarter inch or less in size. Occasionally, there are larger specimens to be had.

One of the largest gastropods we found that was a turriculate form type, was this one in a tan dolomite. Excellent detail can often be preserved in the dolomites, including the growth lines and protoconch detail.

This peculiar looking fossil, is a fossil cattail reed in the center, surrounded by a ring or spiral arrangement of small gastropods all of the same size around the base of the reed. This is an example of the snails laying thier eggs on the stem of the cattail, and some period after they hatch many of them fall to the bottom in a circular pattern. In this case, they were quickly buried by some sort of event, and preserved.

Many of the gastropods found in the Payson basin such as this one found South of Rye, still have a white calcified material lining the shell cavity. This is the remains of the aragonitic shell preserved in the molds.

Fossil cattail reed, with growth lines along its length. Many of the boulders and rocks found in the region contain the tubes of cattails and aquatic plants. This indicates a nearshore condition in only a few inches of water.

Typical plant hash found in great abundance in the Payson basin formation. The partially macerated remains of reeds, grasses, and aquatic plants can be found in great layers throughout the formation. This example here shows many small bits in some limestone found on the north and of the Payson basin.

Trace Fossils

Very fine rhizomes in a nearshore environment created by either aquatic, or or plants that grew just out of the water. The small tubes represent the passages in which the the feeding tendril roots of plants searched through the sediment for water. Occasionally, as we have found in certain areas,some of the larger root tubes contained modified remains of the original roots still intact. Such preservation is rare and outstanding, and uses a glimpse of the ancient root structures which created the tubes.

More typical rhizomes are the larger type, which span up to an eighth inch in diameter. They are less packed than the fine hairlike rhizomes as seen above, and represents more larger root structures probing for moisture.

This large block of limestone found in a creek, is filled with giant rhizomes. It almost looks like Swiss cheese because of the large number of tubes contained within.

Peculiar Fossils

Root Mummies. This 60x view shows the contents of one of the rhizomes we found, that was deep inside a giant boulder and shows the modified remains of the rhizomes progenitor. Although they have shrunk down considerably to a smaller size, they were quite abundant in some areas deep within the insides of the rocks.

A better view of another root mummy, which has shrunk to about a quarter the size or less of the original rhizome cavity. Higher magnifications revealed an extremely strange appearance which was withered, and twisted. We have never seen anything like this before, and plan to pursue this further in our outings.

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