Either pay it and forget about it or go back to Oregon on your court date and try to defend yourself and maybe the judge will reduce the fine or throw the ticket out. If you don't do one or the other there will be a warrant issued for your arrest.
If you pay it, do so by sending a US Post Office Money Order--no personal checks--and send it Certified Mail, Return Receipt Requested. Keep copies of the ticket, both sides of the money order and the Certified Mail receipt and the little green stub Oregon is required to send back to you when the Police in Oregon sign for and receive your payment. Keep copies of all the associated documents in a single envelope your glove box, in the event you are stopped in the future and there are any questions about whether you paid that out of state speeding ticket.
The economy here where I live in Florida is bad - tax revenues and tourist income are way down from what they should be. So to make up for it, one of the things our State Government did was to double all speeding ticket and moving violations fines, plus they made huge increases in the prices of driver license renewals and license plates/vehicle registrations. I would guess the economy in Oregon is probably not much better and you may have a hard time in court, whether or not you have a legitimate explanation of your reason for speeding. You may even wind up paying more for the ticket and court costs too.
I would pay the fine, keep good copies of all the documentation and move on. If California allows it, see whether you can go to traffic school in person or online to keep the points off your license and keep from increasing your car insurance premiums.
