Say you are a well-off young doctor visiting San Francisco from your native Vermont in May of 1903. You're looking for a thrill, and you rather like these newfangled automobiles, even though most people think they're a passing fad. You don't own one, you've hardly ever driven one, and there's no AAA to help you, young man. What of it? You buy a car, you hire a mechanic to come along, and you head up the Sacramento Valley and the Oregon Trail, destination back home to Vermont.
You know what this is missing? A dog. Luckily for us, Dr. Horatio Nelson Jackson felt the same way, and picked up a white pitbull outside Caldwell, Idaho. It seems he paid $15 for him, which in 1903 bucks was some sizable investment. Dr. Jackson named him Bud Nelson, got him a pair of doggy goggles (don't forget, the whole car was open in 1903), and the rest is history. History that I never knew till this morning, but Ken Burns has gotten there and made the movie ahead of me. Have a look!
Spoiler: Bud lived with the Jackson family happily ever after; Dr. Jackson got busted once for speeding - over the 6 mph limit.