See the context of this sign.

Fractured Dacite

The mudflow that poured down the flanks of
Lassen Peak on May 19, 1915 into Lost Creek and
up onto this general area carried boulders of the
Lassen Peak dome and hot boulders from a small
dome that formed in the summit crater during
May 14-19, 1915. A virgin pine and fir forest that
once was here was pounded to splinters by a
massive hot avalanche that occurred just minutes
before the mudflow.

As this "hot rock" cooled, its exterior shrank and
cracked causing the boulder to split. As the forest
reclaims this area, it becomes more difficult to
recognize the events that occurred here in May
of 1915.

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