Around kilometer 900 on ruta 147 (about one hour from San Luis), you will find this wonderful park. One can do simple day hikes, hike into the canyons with a guide (required), and even camp in the park. Guides will take you in the morning, before 10 or 11, and after 3pm, assuming there are no heavy rains and the temperature does not get above 36C. Two liters of water is a must (and a minimum).
On the summer day we were here, the temperature reached 41C (106F). Although the guides were eventually allowed to hike down when the clouds rolled in and the temperature dropped, we were already on our way to do the 1–2 hr day hikes.
We walked the Sendero Flora and Sendero Miradores Balcon Sur, Potrero de la aguada, with a view of the Farallones rock formations. All this was once part of the Camino de los Dinosaurios and plenty dinosaur skeletons have been found here.
I plan to come back in winter and do the 10km hikes into the canyon in colder days.