"The earthen oven at the Blue Ox Millworks in Eureka, California was constructed in 2004 by Appropriate Technology (Engr305) students at Humboldt State University. The project took four, three-hour work sessions to complete over a total of four weeks. As of 2007 it is still standing, is in immaculate condition and retains nearly the same heating efficiency as when it was first constructed. This page includes information on the construction of the Blue Ox earthen oven and information and updates on its current condition."
http://www.appropedia.org/Blue_ox_earthen_oven