See the context of this sign.

Avalanche Boulders

The Devastated Area was formed by a volcanically
triggered avalanche and mudflow on May 19, 1915
and by the pyroclastic flow and mudflows on May
22, 1915.

The large black dacite boulders on this hillside are
pieces of a small dome that filled the crater on top
of Lassen Peak between May 14 and 19, 1915.
During the eruption, this dome was torn apart and
the fragments were thrown out onto the steep
snow-covered slopes. Melting snow slid down the
mountain entrapping these boulders in a fast-
moving avalanche. Tumbling and rolling on smaller
rocks and pebbles, these sizzling 50 to 100 ton
boulders came to rest on this hillside.

Don't miss the rest of our virtual tour of Lassen Volcanic Park in 1699 images.