They might be Giants: Colossal lacustrine stromatolites.

The article discusses a study which describes the giant stromatolites that occur in the Green River Formation deposited in alkaline lakes that covered much of Wyoming, Colorado and Utah for several million years in the Eocene. Topics covered include a description of stromatolites and other microbialites from a paleontologic and astrobiologic perspective, the different properties of stromatolites that are critical to oil recovery, and stromatolites as paleoenvironmental records.