I will certify that Temecula is absolutely 100% infested with Black Widows – I go on hunts at least 3-4 times a week to keep them under control.
They are of course native to the valley, but as I understand the wineries really pump up their numbers.
As an expert in eradicating Black Widows, I have never seen one make a nest at ceiling height. Black Widows in my experience make their nests/webs lower to the ground – occasionally I will see them 3-4 feet off the ground but never much higher.
They are easy to spot at night with a white LED flashlight.
Also, Black Widows are VERY GOOD at detecting threats – you have to be fast.