RE rock dome ovens.  The Californa motherlode area has numerous rock and
brick domed ovens built by Italian immigrants to bake bread in a traditional
manner.  Julia Costello has been researching these ovens and recently
presented a paper at the SHA on them, in the Storytelling session.  Priscilla
Wegars also has information on similar structures used to bake bread.  I
think these may have been related to railroad workers hailing from Greece(?)
 
UNR Basque Studies center has been working with the Tahoe National Forest to
repair and construct several dome shaped ovens that were built by Basque at
sheep herding camps in the Sierra.  They are very similar to the Italian and
Greek structures and were used to bake circular loaves of bread for delivery
to the Basque sheepherders.
 
Your ovens sound like traditional bread baking structures catering most
likely to the Italians working on the railroad.
 
Mary Maniery