Green River Formation

United States

The Green River Formation is an Eocene formation occurring in present-day Colorado, Wyoming, and Utah.

It is a lagerstätten, a site of fine fossil preservation.

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The Green River Formation is one of the best preserved fossil sites in the world, and is incredibly well known amongst collectors.

Fossils found here include various types of fish, stingrays, paddlefish, gars, catfish, bass, frogs, salamanders, snakes, lizards, crocodiles, turtles, birds, bats, rodents, primates, spiders, ticks, scorpions, shrimp, weevils and bugs of many kinds.

Probably the best known fossils from the site are Knightia, a genus of bony fish which are often sold on plates. They are the state fossil of Wyoming and the most commonly excavated fish fossil worldwide.

Slabs can often contain more than one fish fossil, with some fine specimens containing dozens or more.

Among my favourite fossils from the site are flies, fish, leaves – but palm fronds, flowers, and stingrays are high up on my dream fossil list.

It is worth noting that sometimes fossils from this (and other) formations with pale coloured matrix are sometimes painted or stained with tea in order to make them look more complete or solid than the simple bony fish.