“...The South Fork of the Crooked River is a famous location for limb casts that have many interesting features. They often have green moss in clear to white tortoise shell agate and they also have famous black dendrites that lie like black tree branches just below the skin of the specimens. The moss in the original specimen, which was about a foot in diameter, occurs in long branches in clear to whitish agate..”

From the webpage of Thom Lane theagatetrader.com