Old Faithful Geyser of California
Old Faithful Geyser is about a 2h30 drive north of Stanford.
This geyser erupts every 15 to 55 minutes and can reach a height of 80 feet depending on the time of the year (December-February, every 5-15min with a maximum of 35ft; March-May and September-November, every 15-35min with a maximum of 50ft; June-August, every 25-55min with a maximum of 50ft).
Old Faithful geyser is located on private property, so there is an entrance fee of $15 per adult.
There are also llamas, goats, and sheep, as well as a geological museum and a nice resting area with seats. So, you can hang out with the animals, learn about the geyser, or relax in the resting area while waiting for the geyser to erupt.
It may not be the most impressive geyser in the world, but if you have never seen one, it is quite exceptional.
After your time at the geyser, you can spend the rest of your day in Calistoga, Sonoma, or Napa (See Wine country page).