Inscription:

Compañero estudiante:
Nunca olvides la sangre
generosa de los martires
universitarias caidos en
l>as gloriosas jornadas
de marzo y abril de 1962 que se inmolaron por darte
una patria mejor
5º aniversario – A.C.D.O.
Quezaltenango, 21 abril 1967

English translation:

Fellow student:
Never forget the blood that was spilled here by the university student martyrs that fell on those glorious days of March and April of 1962.
They sacrificed themselves to give you a better nation.
5th anniversary - ACDO
Quezaltenango, April 21, 1967

A brief Google search didn’t turn up much information about the protests. The best I have is the brief summary on hmdb.org:

Regarding 1962 Student Protests in Quetzaltenango. In March and April, 1962 there were widespread protests throughout Guatemala against then-President General Ydigoras Fuentes, who was widely seen as having been elected in corrupt elections. There was also considerable anger for Guatemala having allowed the U.S. to train Cuban exiles in Guatemala for the 1961 Bay of Pigs invasion. In this early phase of the Guatemalan civil conflict, that would go on until a formal peace treaty was signed in 1996, it was common for student protests to be met with intense violence by military forces, resulting in many student deaths. In future years the conflict would generally move away from urban centers and towards more rural areas.

https://www.hmdb.org/m.asp?m=100773