Hello ri003rj6 and welcome to JustAnswer.
Unfortunately, mistakes like this neither invalidate the ticket nor provide a defense to this particular charge. Here's why:
In California, the maximum speed law limit (Vehicle Code section 22348, subd. (a)) makes it an infraction violation to ever drive above the maximum speed limit, which is normally 65 miles per hour, even if it is otherwise safe to do so.
Vehicle Code section 22356, subd. (a), allows the California Dept. of Transportation to make the maximum speed limit 70 mph on certain highways (typically freeways) if particular conditions exist. When the posted limit is 70 mph, it is a violation of section 22356, subd. (b), to go faster than 70.
If an officer makes a mistake such as the one you described, the citation can be amended by the court at any time to correct the mistake and reflect the true violation.
Therefore, what will almost certainly happen if you write to the Siskiyou County court (a procedure which is not otherwise authorized in any event, though many judges will consider informal letters from out of state traffic defendants) is that the judge will either take you word that the true speed limit was 70 not 65 or, at the very least, confirm via the CHP or court's own records of the speed limits in the county, that the true speed limit was 70. Then, the court will amend the citation to state the correct speed limit.
If you were charged with a violation of Vehicle Code section 22348, subd. (a), violation of the 65 mph maximum speed law, the court will then amend the citation to charge a violation of Vehicle Code section 22356, subd. (b), violation of the 70 mph maximum speed law.
The fine that would be imposed will likely be the same in either event and a letter alone, even if considered by the court as I described above, will not result in a reduction of the fine.
The correct procedure to follow, if you do not want to have to travel back to California to contest the ticket, is to request a trial by declaration. Information about all Siskiyou County traffic court procedures is available on the court's website at:
Scroll down to the trial by declaration to find information on that process. You will see that you have to call the court traffic clerk's office to request a package of forms that must be completed and returned to the court. On that page, click on the "Contact Us" link to the left for the clerk's office telephone number. Doing so will take you to this page:
The contact number is XXXXX the end of the first paragraph on that page. I would put it here for you, but posting phone numbers in our answers is not permitted.
Be aware, however, that if you elect a trial by declaration and provide the same information in the declaration as you provided here, you will still be convicted, as I described above. Other than a bona fide medical emergency or other extreme exigent circumstances (say, for example, fleeing a fast moving fire or trying to escape from a criminal assault), there is no defense to driving faster than 70 mph on any California highway.
Therefore, you might want to consider the other alternatives described on the court's website, notably traffic school.
Good luck with this situation. If you have any other questions about it, please let me know.