Close up shot of one of the larval host plants of the California tortoiseshell, snowbrush (Ceanothus velutinus) growing in a canyon near Leavenworth, Washington.  When looking for caterpillars, either seek small clusters of black spiny larvae or look for larger larvae.  This host also feeds larvae of the pale swallowtail, hedgerow hairstreak, spring azure, brown elfin, and other butterflies.