Geschichte: Outside of El Paso, Texas: I was hiking in the Franklin Mountains, which, according to the description at the registration point, should allegedly be a range of Precambrian mountains. However, I found this stone containing a petrified ammonite. To me, this specimen looked more Phanerozoic than Precambrian and furthermore I doubted that I just discovered a species which was able to time travel.
Geologie: The Franklin Mountains are actually a range of Precambrian (older than 550 million years) to Pennsylvanian (late Carboniferous, 300 million years old) rocks. That explains the presence of a macroscopically visible fossil animal within the rock. Although this is neither the biggest nor the most beautiful specimen I've ever found, it visualises that some geological information shouldn't be trusted blindly .