When I owned my home and the value went down, I requested the county reassess the value of my house and they lowered my property tax. Of course, when the value of the house went back up, they re-assessed it again higher.
I would think they would assess the value based on other homes in the area, not necessarily what you paid for it, if you got a screaming deal. But in Temecula, since so many places have gone down, I imagine that’s not going to be a big factor and the assessment will be lower, hence so your property tax bill.