Toast the chiles and rehydrate them in 2 quarts of warm water.
Drain the chiles, reserving 2 cups of the water, and transfer to a blender. If it is not bitter, add the reserved chile water; otherwise, add 2 cups of plain water.
Add the garlic and salt to the blender and puree. Stir in the oregano.
Notes
Serve with tortilla chips, enchiladas, grilled or roasted meats, chicken, and grilled shrimp.