The North Face of Rocky Butte
The Grotto is located on the north face of Rocky Butte, an extinct cinder cone which erupted sometime between 285,000 and 500,000 years ago.
It is part of the Boring Lava Field, a series of volcanic vents and flows located in Oregon and Washington.
A basalt cliff spans the north face of the butte, and cuts through the property of the Sanctuary of Our Sorrowful Mother, more commonly known as The Grotto because of the cave carved out of the basalt cliff 100 years ago.
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