In the the Big Bend region of Texas, near the Big Bend National Park, comes reports of a dinosaur-like creature that has been dubbed the Mountain Boomer because of it's booming sound. The Mountain Boomer might be bipedal (walking on two legs). It possesses long back legs, and short front legs. It's about 5 to 6 feet long. It's color is greenish or brownish.
Jimmy Ward claimed to have heard tales of a "giant lizard that walked on its hind legs and whose voice sounded like the roll of distant thunder."
In the early 1970's, someone said that a dinosaur ran a car off the road.
In 1993, someone else saw a Mountain Boomer scavenging a road kill. The "creature" ran off when this person's vehicle came close.
Is it a lizard? Read the below paragraph for some more insight.
Crotaphytus collaris is a North American lizard that can reach a foot (30 cm) long in length (including the tail), with a large head and powerful jaws. They are well known for the ability to run on their hind legs, looking like small dinosaurs.
It's possible the Mountain Boomer could be a dinosaur, while it's also possible that it could be a lizard. But, this North American lizard "can reach a foot (30 cm) in length," while the Mountain Boomer cryptid is reportedly 5 to 6 feet long.
Sources: Dinosaurs: Dead or Alive? O'Donnell, Phillip Xulon Press 2006 and http://en.wikipedia.org/wiki/Common_collared_lizard