I've been washing natural limbs and branches, giving them a light once-over with a small scrub brush and then letting the excess water dry off.
After a drip-dry, I lay it in the oven and set to "preheat" at 300oF. When the preheat light goes out, I turn off the oven, open the door and and leave it in. I remove it when I can handle it with bare hands.
One must be very careful heating wet rocks beyond the boiling point and it's not recommended. If one feels compelled to sterilize this way, temps should be brought up gradually to allow the water vapor to escape before dangerous internal pressures can occur.
It is well known among campers that laying a wet rock in or along the fire perimeter can cause an explosion due to steam pressure.