Hello, Zach,
Thank you for your submission, I have two possible identifications, one that I believe is more probable than the other. It is difficult to give an exact identification as the images provided do not have high resolutions, and it is difficult to see details. But, from what I do see, I strongly suggest you have an in-person assessment made with a regional geological society, museum, or university department.

1. From the images submitted, the example is an ichnofossil. Most sinuous shapes are trace fossils. Trails of worms, snails, and other invertebrates can be preserved as fossils and leave a sinuous shape. Often the shape is the same color and texture as the surrounding rock. This would be from the Jurassic or early Cretaceous period. A FMV on an example from this region and of the given dimensions: 6.5”x 3.5”x 2.25” would be $50- $100

2. I believe further investigation is needed, and again, contacting a regional source would confirm; but I do think this may be a petroglyph or pictograph shard of a snake or other creature. A petroglyph is an image created by removing part of a rock surface by incising, picking, carving, or abrading, as a form of rock art. I cannot access the era or civilization affiliated with the item. I've attached an academic journal article on the region's recent archaeological discoveries. The article also contains images, for your review: https://www.dargnet.org/Publications/CapsSpringRpt_redacted.pdf?

If the item is identified as a petroglyph, cultural heritage protections at the state and federal level restrict the sale of the item. But what a discovery! If it is identified as a petroglyph it would be a welcomed contribution to a museum or university collection. Another possibility is repatriation to the identified tribal nation of origin.