Jean,
Thanks once again for your help.
According to Oman, Franceschi caught La Romana’s rearguard at La Trepa near Osoño and routed it. Oman, vol II, p. 194. Le Noble (pp.104-5) reports the 15e leger were involved in addition to the cavalry division.
As I understand it, in Galicia today, place names are often shown with both versions of the definite article A / La Trepa Coruña etc.
Best wishes
A