The bedrock of Squak Mountain is made up of rocks that formed from sediments carried by rivers into an ancient coastal estuary, where their increasing weight caused the land to sink, only to be buried by even more sediments. In time, the sedimentary layers accumulated more than one mile of thickness. As the sediments slowly collected, sub-tropical forests flourished on the landscape. Trees died and were buried before they began to decay, slowly converting into peat. Further burial and heat, possibly from regional molten magma intrusions in the Cascade Mountains, reduced the water, methane and carbon dioxide in the peat, and changed it into coal. The coal seams are found today in a layer of sedimentary rocks that geologists have named the Renton Formation.

bedrock of

Miocene (Wikipedia) The Miocene (/ˈmaɪ.əsiːn, -oʊ-/ MY-ə-seen, -⁠oh-) is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words μείων (meíōn, “less”) and καινός (kainós, “new”) and means “less recent” because it has 18% fewer modern marine invertebrates than the Pliocene has. The Miocene is preceded by the Oligocene and is followed by the Pliocene.

Squak Mountain State Park History (parks.wa.gov) A generous land donation and the hard work of community activists has ensured that Squak Mountain State Park will be an enduring piece of wilderness close to the homes of millions of urban residents.