I am going to add some extra views of different structures.
In California there are three Webspinner species to choose from:
Chelicerca rubra is the one native species. It is smaller that 8mm, thus eliminating the "Red Webspinner"
Thus it is either a female Black Webspinner. Females have a feint pattern on their heads but a mostly uniform brownish color on their body.
or it is a female / parthanogenetic of the Haploembia solieri "Pink Webspinner" species. The are well known for there distinct reddish colored markings over their pale bodies.

A classic Haploembia solieri was contributed by Harsi Parker sometime ago:

I believe my webspinner is probably also Haploembia solieri. I'm not sure why there is such a variation on how light colored the base color is. And how come sometimes the markings are very distinct. You can make out the flames on the head. I guess the biggest factor is that all of the black webspinners sighted in California have been in southern California. The Haploembia solieri species is from the Mediterranean and shares a similar climate.

However, it would be nice if someone with more experience could confirm this.