The Francia is a 25 km long tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Alagón, a right-hand tributary of the Tagus

Tagus

The Tagus is the longest river on the Iberian Peninsula. It is long, in Spain, along the border between Portugal and Spain and in Portugal, where it empties into the Atlantic Ocean at Lisbon. It drains an area of . The Tagus is highly utilized for most of its course...

. Its source is at 1350 m in the Valle de Lera (Sierra de Francia

Sierra de Francia

The Sierra de Francia is a mountain range located at the southern end of province of Salamanca, Castile and León, Spain. It is located about 70 km from Salamanca city, the provincial capital....

). It flows into the Alagón at a height of 420 m.

The importance of this river lies in the fact that it gives its name to the Sierra de Francia, south of Salamanca

Salamanca

Salamanca is a city in western Spain, in the community of Castile and León. Because it is known for its beautiful buildings and urban environment, the Old City was declared a UNESCO World Heritage Site in 1988. It is the most important university city in Spain and is known for its contributions to...

. Part of its course falls within the Las Batuecas-Sierra de Francia Natural Park protected area

Protected area

Protected areas are locations which receive protection because of their recognised natural, ecological and/or cultural values. There are several kinds of protected areas, which vary by level of protection depending on the enabling laws of each country or the regulations of the international...

.