The Bermuda grass you have in your yard is very good nutrition for desert tortoises. You can also find other good native grasses and weeds listed in this Arizona game and Fish brochure specifically for desert tortoises:Hi yes i've been going to the websites looking at different ideas for food and what not I'm just not 100% sure on the food just because the only thing I've been seeing them he is either my Bermuda grass that I have growing in my backyard or the Romain lettuce but I know Romain lettuce does not have the nutritions they need so I'm trying to figure out other ideas as well another thing is I'm trying to also figure out what kind of tortoise it is I know someone did tell me that they are desert tortoise but also a different kind not too sure but then again I get caught up in reading on everything about tortoises so I get sidetracked it so very interesting
http://www.azgfd.gov/w_c/tortoise/documents/NativePlantsforDesertTortoises_2008.pdf
a good source of seeds (they even have a desert tortoise wildflower mix):
http://shop.nativeseeds.org/pages/seeds
They will eat a variety of greens, which is very healthy. You may plant recommended grasses are weeds and find that they won't eat certain ones for a year, and then find that suddenly they are gobbling down what they passed by for some time.
Good luck with your adorable little tortoises.