I'm thinking brown area being Silverhorn. And yes a great deal of the natives who can trace their families back to the earliest days of the area are unicorn but given that there is a great deal of labor and work to be had is a mining area such as this I'd say the earth pony population is not insignificant, but largely come from other territories to the silverhorn lands for work opportunities. Pegasi would defiantly be a rarity at best give a great deal of the work being done under ground. 

As for the their banner...I'll get back to you on that...but I'm also open to suggestions xD