San Marcos police said an 18-year old woman died early Tuesday after being struck by an Amtrak train while she was walking on the railroad tracks.

Police said Angelina Isabel Castillo, of San Marcos, was walking on the tracks at Post Road and Aquarena Springs Drive just before 11 p.m. Monday when she was hit.

Castillo was taken to Central Texas Medical Center where she died shortly after 1 a.m. Tuesday, according to Sgt. Christopher Tureaud.

An autopsy has been ordered.

According to police, Castillo's death is being investigated by the San Marcos Police Collision Investigation Team, Amtrak Police and Union Pacific Police.