This type of fossil is usually attributed to annelid worms ingesting sediment. This is by far the rarest fossil found, we have only encountered two sets to date in some hundred hours of exploration of promising beds. Obviously subareal exposure, this slab also contains mudcracks as well. Here we see two toes of a small mammal, perhaps some type of feline or canis species. Rhizomes - A very recent find here, along a roadcut along I17 near Black Canyon City.
Rhizomes are the tubes and tunnels left by a living plant as it searches for water in the sediment.
Because the plant is still alive when old tubes are abandoned, they are considered by most paleontologists as trace fossils. These are preserved in volcanic ash, and are made of the same material. The most predominant sedimentary structures found in the Chalk Canyon formation are lithified mud cracks. Formed when a shallow pond or lake dries up, and the resulting cracks become buried in more mud, they literally fossilize. This image is of the larger type found, the scale at bottom is as all images in centimeters.