Take I-75 NORTH, from Ft. Myers, to I-10 WEST to TALLAHASSEE off EXIT 435 in Lake City.
Take I-10 WEST all the way across the country to CA-210 WEST to PASADENA off EXIT 77C in CALIFORNIA. To bypass NEW ORLEANS, take I-12 WEST (EXIT 259B off I-10 in LOUISIANA). To bypass PHOENIX, follow the PHOENIX BYPASS ROUTE (I-8 WEST [EXIT 199 off I-10 in ARIZONA] to AZ-85 NORTH [EXIT 119 off I-8], and then AZ-85 NORTH back up to I-10 WEST towards LOS ANGELES).
Take CA-210/I-210 WEST, around LOS ANGELES, to I-5 NORTH to SACRAMENTO at EXIT 1A.
Take I-5 NORTH to I-580 WEST to SAN FRANCISCO at EXIT 446.
Take I-580 WEST to I-80 WEST to SAN FRANCISCO at EXIT 19A.
Take I-80 WEST, across the BAY BRIDGE, into San Francisco.
Answer: Northern California is considered to be from Santa Barbara north to the Oregon border. It is approximately 650 miles north to south. Why they consider Santa Barbara northern CA, I have no clue! Most people who live in northern CA (like myself) consider Northern CA to be from about Stockton northwards, which is about 300 miles.