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The River Arlanza is a tributary of the River Arlanzón.
It rises
in the Sierra de la Demanda, near Quintanar de la Sierra in an area known as Fuente Sanza.As it
flows through the province of Burgos, it passes through the
municipalities of Castrovido, Salas de los
Infantes, Covarrubias and
Lerma.It joins the Arlanzón near Quintana del
Puente shortly before the Arlanzón itself joins the River
Pisuerga.