It is named after a nearby shale formation formed by a creek.

This is particularly useful in shale formations which do not have sufficient permeability to produce economically with a vertical well.

When the ash happened to fall into lakes, it created widespread shale formations.

Situated 45 miles north of the Painted Hills, it sits on the same shale formation and shares the fossil record.

Long after the post office creation, the name was applied to a nearby shale formation.

Cuadrilla's bore passes through an aquifer before it reaches the shale formation.

But there's nothing to worry about, the agency says, because "Groundwater is not present in the shale formation at the Preese Hall site."

Midway up there is a stone terrace, with a narrower shale formation rising out of it.

The shale formation is approximately 20.23 feet in diameter at its base, and between 25 to 30 feet at the top.

Preserved within the shale formations are plant, animal and insect species that inhabited the area over 50 million years ago.