The Georgia metalheads in Mastodon have built their 17-year career on a reputation for delivering sludging, heavy-handed, technically challenging arrangements that have become metal classics such as 2004’s Leviathan and 2006’s Blood Mountain. Since then, though, the quartet have drifted toward more melodic, progressive rock, such as their recently released Emperor Of Sand, a concept album about a doomed desert wanderer. While the sound is a departure from their origins, it had the most successful Billboard performance, charting at No. 7. And even if the music isn’t as heavy as their original fans might like, this show at Gas Monkey Live! is nevertheless an opportunity to see one of the most technically gifted metal bands in existence. And with Eagles of Death Metal and Russian Circles also on the bill, the rock world is well represented.