Step 1Hold the California and ancho chiles under running water to rinse. Use scissors to cut off the chiles stems and cut the chiles in half. Shake out the seeds onto a paper towel. (Put the seeds in your garden for the birds.) Place the chiles and garlic in the top half of a steamer set over simmering water. Steam for 25 minutes. This technique, as opposed to soaking dried chiles in boiling water, preserves more of the chile flavor.
Step 2Remove the chiles from the heat. Place 1/3 of the chiles in a blender with 1 cup of water. Puree until smooth. Pour the puree into a wire strainer nested over a large bowl. Continue pureeing the rest of the chiles, garlic and water as in the previous step, in batches, so that each time you add 1/3 of the chiles. Push all of the chile puree through the strainer using a spatula or wooden spoon. Be sure to scrape off the chile puree clinging to the bottom of the strainer. Pour the remaining water into the blender and turn it on to help clean the blades. Pour this chile water through the strainer to catch the last bit of goodness. You should now have about 3 1/2 cups chile puree.
Step 3Heat the olive oil in a deep skillet over medium heat and add the flour, toasting lightly until light nut brown, stirring, 4 to 5 minutes. Whisk in the chile puree and add the oregano, vinegar and salt. Simmer the sauce for 20 minutes to blend flavors. Taste, and if the sauce seems a bit sharp, add sugar. If the sauce seems thick, add water or broth, simmering again for about 5 minutes.