Black widow
A brown spider that has a white diamond on its back is known as a Parson spider. This spider does have a mildly venomous bite.
John Muir, Yosemite and a bird
A quick check of the US Mint's site reveals that the back of the 2005 California quarter depicts naturalist John Muir, a California condor, and the Half Dome rock formation in Yosemite Valley.
California uses the same coins as the rest of the states, with Lincoln on the penny and Washington on the quarter. The California state quarter has John Muir on the back.
The spider you are describing is mainly found in Australia. Its called a red back. Very Very Poisonous.
The spider you are referring to is likely the yellow sac spider. Yellow sac spiders are brown with two yellow stripes on their back and are commonly found in California. They are not considered aggressive towards humans but can deliver a painful bite if provoked.
because the quarter back has a quarter of the job
Spider is light brown with gold or yellow diamond back
A black widow spider is black with a red mark on it's abdomen; this might or might not be what you meant. The black widow sometimes has a red mark on her back, as well. The red backed spider of Australia, a relative of the black widow, has an orange red mark on the back.
Black House Spider is similar to one I found with diamond like shapes on their back. They're about 1/2 inch in body length, with long noticeably hairy legs. Semi-venomous, not fatal to humans.
On the back of a quarter is an eagle.
A false widow spider is a spider that is known to have a skull depicted on its back. This spider also has orange legs.