However, there's a delay between when you close escrow and when your property tax "rebalances", which you can read about below (be sure to read about tax-lowering Prop 8 as well):
"Estimating Property Taxes in CA"
So I'd first find out an address you are interested in in Portola, check out the assessed value with that link, then call up the treasurer's office and get a breakdown of the taxes sent to you, check out the exemptions (they are listed on the assessor's website), and then you will be able to calculate the exact annual property taxes on that home given $X sales price.
http://www.countyofplumas.com/index.aspx?NID=102 has the link to check assessed values in Plumas County. You can call up the county treasurer office and ask what property taxes are for a specific property and they'll fax you the breakdown so you can see the basic levy rate along with any special assessments. http://www.countyofplumas.com/index.aspx?nid=95 is the link to the Plumas County treasurer/tax collector.