That is one of the recluses, there are three that are now in the US, the brown is a native and the males are quite thin bodied but the females have a thicker abdomen, in Dade county , Florida there is an import, the chilean recluse that is a bit smaller and paler, very similar to the one found in LA, TX, and acouple times in CA, it is the Meditteranean recluse, all have the fiddle back and same eye pattern and leave similar bites. The bites often lead to systemic infection that can kill.
Another spider spider that is a problem up in the northwest is the aggressive house or hobo spider, as it's name implies it is prone to bite. I have been bitten by one and while not as bad as a recluse the lesion is a necrotic sore that continues to grow until repeatedly debrided and supportive antibiotics are given, mine lasted over a month with treatment and got about 1 1/2" across and in the center muscle tissue was exposed. again the female is heavier.
The yellow sac spider of the north west give a painful, necrotic bite as well but the lesions usually don't exceed an inch wide and will heal on their own. Males are tiny and not known to bite.
Here is the recorded distributation of the hobo and recluse spiders, and pics of the three spiders
