Strange markings

Since I moved here 32 years ago I've come to realize that the San Joaquin Valley is probably the Black Widow Spider Capitol of the World. I've seen lots of these little critters, but they are easy to avoid if you understand their habitats. I caught this one on my fence this morning, and she is evidently moulting. As the lighter carapace spreads and turns black, the lighter areas of the juvenile spider create some very strange markings before they disappear completely. On the underside, however, you can clearly see the characteristic red hourglass.