As soon as my son saw this he cried "Snakes!!" and keep warning his mom and dad. He doesn't know how to read very well due to his autism, but he surely understands the pictures and he well knows snakes bite and can kill. They have these posted everywhere because during the summer months all this ruins and rocks are a haven for them to hide from the shade. Plus, stones keep somewhat a cool from the night air, so during the day they love to sleep near them. Over 800 people are bitten every year just in California and sadly three of those die from the venomous ones. I well know around my own property I have to be careful and I am constantly reminding my boys of the dangers. So Please be careful!!!
As enticing it is to explore and we all are curious creatures, but please stay out and do not walk into or crawl aroung the ruins. They are crumbling upon themselves every day. I tried to keep a safe distance, but also found myself getting way to close to the structures. So please be aware.
Watch where you walk as rattlesnakes are present. It is advised not to go inside the buildings, since they are crumbly. If you do though, just be careful. Deffinately stay out of any abandonded mineshafts as they can be extremely dangarous.