Blue Diamond Hill is one of those 'sleeper' hikes that not a lot of people know about. That's a shame because the stellar view and relatively easy access make this one of those must do hikes for Las Vegas! The view from the top of the entire Las Vegas valley and all of Red Rocks is stunning.
To get to the trailhead from Las Vegas. Take Charleston Blvd west into Red Rocks. Go past the entrance to the loop road (Red Rocks Visitor Center) 1 mile to the Horse Riding corral on the left. Park here.
A full route description is available in the book Afoot and Afield: Las Vegas and Southern Nevada guide book. Basically the trail wanders E-S/E from the horse corral up into a canyon, then turns east and heads up to the ridge overlooking Las Vegas. About half way up a side trails heads off to the left and heads up through an area I call 'rock city'. This gets you to the view of Las Vegas faster but you miss the cool canyon and fossils contained there. There is really no true summit to Blue Diamond, the entire eastern ridge of Blue Diamond Hill is the summit. This route ascends about 1700 feet in two miles.
Good shoes, water, your camera.
Trails.com has the only route description for this hike I could find. It's a members only site. Rather than steal their information regarding this hike I have just put the basics in here. You'll figure it out.