Prop 13, Prop 60, Prop 90
Prop 13 is when you pay 1.25% of the purchase price for the life of your home or until it transfers ownership via sale.
Prop 60 is when you (as long as either spouse being 55 yrs of age or older) takes advantage of transferring your lower tax base of your existing home to a purchase of a new home (as long as the new home is at equal or lesser value of your old home) WITHIN the same county.
Prop 90 is when you do the above (Prop 60) across county lines. At that point you need to figure out if the county that you're thinking of purchasing at (in this case Riverside County) still participates in this program.
There are currently only 8 counties in California that still participate in Prop 90. Unfortunately, Riverside County is one of the counties that has dropped out of this program.
All counties, however, still participate in Prop 60 (where you CAN transfer your old tax rate WITHIN the same county)
And all counties still participate in Prop 13 (where you pay 1.25% of your purchase price if you don't partake in either Prop 60 or Prop 90).