Toast the chiles and cumin seeds according to the instructions above.
Using a set of kitchen shears, cut the chiles into small pieces.
Add the cumin seeds, Mexican oregano, and granulated garlic to your spice grinder and grind until powdered.
Working in batches, grind all of the chile peppers into a coarse powder. Mix together and store in an airtight jar in a cool dark place.
Most home spice grinders only hold a small quantity of ingredients, so you'll need to grind the chiles in a few batches then mix them together afterward.If you want to be able to knock it all out in one batch and in just a few seconds, a C Goldenwall grinder can do it easily (it's what I use).