Here is a good web site on the effect on animals
http://www.oilspill.state.ak.us/notebook.html
As far as the effects on humans, you can only be affected if you eat or drink the oil. Unlike, animals, humans know how to avoid oil spills and don't get affected very much. They can be affected if they eat animals that have eaten oil, though. But not much is known about these effects. Usually, animals are tested and people are told if there is too much oil in the animals.

Oil spills can be dangerous in the short term because the damage eyes, lungs, and gills and because they mat down fur and feathers, making it difficult for animals to keep warm or fly.The oil kills small animals in the water immediately. Oil globs that sink kill bottom-dwelling animals like crabs and clams. It can take 3-10 years for an area to recover. In the long term, less is known about health effects. What effects do you see? Do people use the beach less? Note that in the Santa Barbara County area, petroleum has been washing up on the beach since long before drilling. The early residents of the area (such as the Chumash) used the tar to seal their canoes. If the petroleum is "natural" is it any less dangerous?

Here are some articles about the Guadalupe spill:
http://www.sanluisobispo.com/stories/0498/guad_spill_prot02.html
http://sddt.com/files/librarywire/98/07/22/1k.html
http://www.sanluisobispo.com/stories/0798/guad_spill02.html

Thanks for asking.

I have heard about the oil leak at Guadalupe. It was a pretty major event. I have found lots of info on the web using this type of a search: +Guadalupe +Unocal +oil leak. Here is an informational statement off the Surfer's Alliance Web page: "Unocal leaked between 8.5 million and 20 million gallons of a petroleum thinning agent called diluent at the 2,700-acre site, making it one of the largest land-based oil spills in the history of the nation. In July, [State Attorney General Dan] Lungren announced a settlement in which Unocal agreed to pay $43.8 million in fines and damages." The immediate threat to your town was contamination of the ground water by the diluent. This apparently did not occur, but you should double-check that. Secondary concerns were to marine and nearby terrestrial organisms and their environment, which of course were adversely affected. I am not specifically knowledgeable about the adverse effects of the diluent to the marine and terrestrial life. But, if you eat seafood from the immediate area then you might be affected. If you frequented the beach were it occurred you would be affected (the beach will be "contaminated" for years). Also, I'll bet Unocal has had to provide the public of your town with the exact information you are interested in. Look up Unocal locally and try calling and requesting info regarding your concerns. For general info on effects of oil on marine life, an on-line search would be your best bet. But remember the Unocal leak was diluent, not really "oil" and that might change the way it interacts with the environment and its toxicity.

In addition to leaking oil, the 1992-94 leak in Guadalupe also leaked a chemical called "diluent" that is used to make the oil flow more easily. The oil itself is not so bad. It stays underground where it floats on top of the water table and generally won't affect you unless you dig a well and try to pump the water out. Then you might get some oil too. The diluent is more toxic and spreads faster. I don't know much about it.
The whole disaster there in Guadalupe is huge, though. There is more oil and diluent that is sitting underground there than you or I can imagine, and there has been a lot of arguing about how to get rid of it. Some people think that the best solution is to leave the ground the way it is and to inject the ground with special oil and diluent-eating bacteria and nutrients for the bacteria. Then the bacteria can just eat it up. This has worked pretty well in some other places where oil has leaked underground. I haven't heard about the oil or diluent leaking out into the ocean, but it seems to me that it eventually would.