If you're looking for a meeting place or a good stop around ½ or halfway between San Francisco and Eureka, you can try Orrs Springs, CA, which is a little over 2 hours northwest of San Francisco, or about 2½ hours south of Eureka.
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 Geyserville, CA. This is about 1½ hours north of San Francisco.
About ⅔ or two thirds of the way, you can stop at Cummings, CA. This is about 3 hours northwest of San Francisco, or almost 2 hours southeast of Eureka.
About ¾ or three fourths of the way, you can stop at Benbow, CA. This is about 3½ hours northwest of San Francisco, or about 1½ hours south of Eureka.
If you drive straight through without stopping at all, the total distance is 271 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, 47 minutes.