It depends a bit on the size of the rocks/gravel. The number of true tubeless tires that are specifically geared toward gravel riding are still a bit limited. Specialized makes a 33 and 38mm version of their Trigger Pro 2Bliss tires that are file tread in the center and some small blocks on the outside. Last summer I ran the 33mm ones and found myself wanting to run a bit larger diameter so that I could run lower pressures. I then bought some 40mm Clement MSO X'Plor 120 TPI's and ran then tubeless (they aren't designed for this) with some success and some problems, especially with the initial setup. So for this year, I got a set of the 38mm Specialized Trigger Pro 2Bliss tires. I hope to get them out for a ride this weekend, but they should be pretty much like the 33mm version I had previously.
2015 Tamland 1 with RS-685 Shifters
2014 Niner RLT SRAM Red 2014 Raleigh RXC Pro Disc CX Race 2008 Lemond Poprad SSCX Racer 2006 Trek Portland Commuter