The Gifford Shale is not a known geological formation. It's possible you're thinking of a different shale formation or have a typo.

If you can provide more details about the specific location or other characteristics of the formation, I might be able to help you identify it.

For example, do you know:

* Where is it located? (State, country, specific region)

* What are its distinctive features? (Color, fossils, mineral composition)

* What other information do you have? (Geological map, research paper, etc.)

With more information, I can help you determine the age and geological context of the shale formation you're interested in.