Rinse and pick over beans. Combine beans, ham hock, onion, chiles (including liquid), oregano, and salt. Add water to about 1 inch above beans. Bring to a boil. Cover and simmer over low heat for 1½ hours, stirring occasionally.
Add 1½ more cups water and simmer for 2 hours more, or until beans are tender and liquid has thickened. Add more water as necessary.
Remove ham hock and finely chop meat. Stir chopped meat into beans.