Where the Ride A Pet volcano is
Travel past the Desert and cross the water to Volcano Island. The way into the crater is on the right side and can only be reached with a flying pet, so get the Phoenix (or a Griffin) first.
How to get the Volcanic Egg in Ride A Pet
Grabbing the egg wakes the dragon guardian and starts a 20-second timer to escape the crater. Once you are out, a second timer starts — reach your ranch and drop the egg in a nest before it runs out or the egg cracks. A fast flying pet makes both legs much easier.
Ride A Pet magma mutation
You can also dip any egg into the volcano’s lava to try for the Magma mutation (10× speed and money). Each egg gets one try at about a 15% chance; failing costs the egg a few seconds of its timer.