In a dry skillet over high heat, toast the dried ancho chile pods for a few seconds on each side until slightly fragrant and they start to puff up a little. Let them cool slightly, then remove the stem and shake out any seeds. The more seeds left in, the hotter the chili seasoning will be.
Using a food processor, spice grinder or high speed blender (like Vitamix), pulverize cooled chiles into a powder. Work in small batches if using a spice grinder.
Add the oregano, garlic, cumin and optional Chimayo powder. Pulse several times to combine and blend. Store in an airtight container. Makes a little more than 1 cup total.
Notes
For a milder flavor, I also use a mix of dried chiles: 8 Ancho and 4 California.
Mexican oregano is native to Mexico. Unlike Mediterranean oregano, it's a relative of lemon verbena, with mild licorice and citrus flavors.