Plate tectonics have been on the go for more than 250 million years and gave rise to the bedrock geology of Kachemak Bay.

The massive Farallon Plate inched northward from near the equator, past Baja California. Rubbing against the Oregon and Washington coast, it eventually reached Alaska about 48 million years ago. This oceanic plate consists of many layers of a sedimentary rock called chert. The oceanic plate's heavy leading edge slides beneath the lighter North American Plate. The upthrusting continental plate is broken up and the Kenai Mountains thrust upward. This process continues, leading to earthquakes, volcanic eruptions, and the growth of mountain ranges.

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