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.
Argiope aurantia, or the black and yellow garden spider, lives in California and has two yellow stripes running lengthwise down its back. They are not dangerous to humans.
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.
because the quarter back has a quarter of the job
the back of a spider
Daring Jumping Spider http://en.wikipedia.org/wiki/Phidippus_audax
The spider that is black with a white crescent on its back is the Brown House Spider. This spider is often confused with the red-back spider.