This is the northeast part of Iran's Central Plateau, which continues into Afganistan(2). It is bounded northeast by the Kopet Dag mountains along the Turkmenistan border which reach nearly 3,000 meters. The center of Khorasan is just as high, but much of it is lower, particularly some parts near the Afghan border, and the province's west-center and southwest. The west-center is the east end of the Great Salt Desert(3) and the southwest is the north end of the Great Sand Desert(4). There are several large salt marshes in the center and east of the province.
Nearly all of the six million plus people here speak dialects of Persian (Farsi or Parsi).
The only local city with over a million residents is Mashhad, the provincial capital; its metropolitan area exceeds two million. Its golden-domed ninth century shrine for Immam Ali Reza is a world Shi'ite pilgramage site. It was capital of Persia for a time in the 18th century.
See central and southern Iran generally
Early mainstream linguistic developments
Common early religious developments
northeast
east
south
northwest
(1) Formerly Persia.
(2) Officially Afghanestan.
(3) Transliterates from Persian as Dasht-e Kavir.
(4) Transliterates from Persian as Dasht-e Lut.