Mexico's range here is deliberate. Barrancas del Cobre is not one canyon but a system of six major gorges, several of them — Urique among them — deeper than the Grand Canyon, with pine and oak at 2,400 m on the rim and subtropical heat on the floor. The footpaths are working Rarámuri routes between rancherías, and the Chepe railway does the long transitions so the walking days can be spent on good ground.
The Yucatán is the opposite kind of place: one limestone slab with no surface rivers, where rain sinks straight through into a flooded cave system and cenotes are simply where the roof has fallen in. In Baja, the Gulf of California holds roughly a third of the world's cetacean species and a wall of undeveloped desert islands. And in Oaxaca's Sierra Norte, the Pueblos Mancomunados hold the land communally and run the trails, cabins, and guiding themselves.
Country-level constraints that decide whether a date is possible.