I belive the highest point in san mateo county is actually Borel Hill located in he russian ridge osp. Long ridge is unique that it contains the intersection of three counties santa clara, san mateo, and santa cruz. The pimt i think you are referring to is actually a bit lower than Borel. The highest point isn long ridge, turtle rock is higher but falls within santa cruz county, atleast this is how i understand it
I stand corrected i see the pint you refer to on the topo map, interstingly it seems it never has been surveyed for an accurate elevation. Maybe that why it has been oberlooked by those who told me borel is the highest , a number of individuals, curious.