Here’s a list of gluten-free grains, seeds, and flours.
If you know of any others, please share in the comments section and I’ll add them to the gluten-free grain list. Thx 
GLUTEN FREE GRAINS, SEEDS, AND FLOURS
Amaranth
Arrowroot
Bean flours (chickpea, lentil, etc.)
Buckwheat
Cassava (aka Yucca, tapioca)
Coconut
Cornstarch
Cornmeal
Flax Meal
Mesquite
Millet
Montina
Nut flour (almond,pecan, etc.)
Oats*
Popcorn
Potato flour
Potato starch
Quinoa (red, white)
Rice
Sorghum
Soy flour
Tapioca Starch (made from Cassava aka Yucca, but the fine starch vs. course powder)
Teff
Kaniwa
*Due to cross-contamination issues, use only certified gluten-free oats. Also, a certain percentage of patients with celiac disease do not tolerate oats very well. Please consult with your doctor before consuming oats.