Rocks are massive heat sinks. It takes a LOT of energy to warm up something with that mass just a few degrees.

Another thing to consider, and this may affect how your temp guns, FLIR camera, or anything that measures surface temperature, is a substances ability to conduct heat. Take a steel plate, granite rock, cement slab, and piece of wood. Heat them in the sun to 100F on a hot summer day. Touch them and which feels hotter? They are all 100F. I would be curious if these different thermometers would all read them as the same temperature, or if conduction plays a role as well. I honestly don't know how a laser reads surface temperature (or for that matter, if the air temperature that the laser passes through affects the reading).

For practicality, acknowledging that garter snakes experience temperature ranges much more extensive than what our care sheets suggest, we may consider incorporating that into our husbandry, in larger than minimal standard housing. For my animals, I routinely offer temperatures up to 100F because while their POTZ is much lower, they certainly have access to this in the wild. Because I also offer a dynamic environment of dimensions that offers everything they need at temperatures throughout their thermal gradient, I can be confident that offering such hot temperatures only adds to their habitat, and doesn't detract from it.

Ian