To the person who wanted to know if dogs were allowed on the Grotto Trail: the trail is posted no dogs, no mountain bikes.
Truth is that you really wouldn’t want to take a dog down there anyhow, unless you’ve got a champion boulder-hopper. Once you reach the grotto the trail gets sketchy. Not to mention the poison oak, which of course isn’t going to bother the dog any. Just everybody who hugs the dog.