However, due to lack of knowledge about these negotiations, the armed clash between the Peruvian and Colombian forces took place in La Pedrera between July 10 and 13.

The Colombian troops established in La Pedrera had created a permanent camp, which included crops and a set of trenches.

Most of the Colombian soldiers became ill with malaria, yellow fever or leishmaniasis, which led to 11 becoming sick, 22 dying, and leaving 34 unfit for combat at the time of the confrontation.

[3] On July 10, the Peruvian commander Óscar Benavides demanded the withdrawal of the Colombian forces, the refusal caused the first confrontation between both parties.

[10] On the other hand, the Peruvian forces suffered a fierce epidemic of beriberi and yellow fever that caused them to lose up to 30 men a day.