Only two towers, not four. They look to be quarter mile apart and 600-800 feet high, very thin and straight, not tapered. They are on the right hand side of I-15 if you are going towards Utah and a mile or so from the freeway near the Glendale/Moapa exit. They are not on top of a peak per se but behind the first ridge (can't see the bottom of the towers or transmitter building from I-15). They are not painted red & white, just plain gray. The northernmost tower had four flashing strobes, the other just had one flashing strobe on top.
They are definitely not FM broadcast and look too large to be AM phased array. Gotta be Govt or Military. They might be Loran, seem to be the right size for that low of frequency. Thanks...