Dr. Don Kowalski claims that F. intermedia is the most common Fuligo in northern California, but I do NOT recall collecting it (yet). This specimen to too large and when I measured 10 spores the average was 8.2 um. It keys in Farr, as well as Martin & Alexopoulos, to Fuligo septica. Farr states the aethalia for Fuligo septica can be white, yellow, orange, brick red or violet!
Farr, M. L. 1981. How to Know the True Slime Molds. W. C. Brown Co. Pub., Dubuque, Iowa. 132p.
Martin, G. W. and C. J. Alexopoulos. 1969. The Myxomycetes. University of Iowa Press, Iowa City, Iowa. 560p.
This looks like Fuligo intermedia…similar to F. septica, but white rather than yellow.