If you're looking for a meeting place or a good stop around ½ or halfway between San Francisco and Fortuna, you can try Redwood Valley, CA, which is a little over 2 hours north of San Francisco, or a little over 2 hours southeast of Fortuna.
Other possible places to stop near the midpoint include Laughlin, Rowes, and Sylvandale.
About ¼ or a fourth of the way, you can stop at Windsor, CA. This is a little over 1 hour north of San Francisco.
About ⅓ or a third of the way, you can stop at Healdsburg, CA. This is about 1½ hours northwest of San Francisco.
About ⅔ or two thirds of the way, you can stop at Woodman, CA. This is almost 3 hours north of San Francisco, or almost 2 hours southeast of Fortuna.
About ¾ or three fourths of the way, you can stop at Cooks Valley, CA. This is a little over 3 hours northwest of San Francisco, or a little over 1 hour southeast of Fortuna.
If you drive straight through without stopping at all, the total distance is 254 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 4 hours, 27 minutes.