Lake Chapala, presently at about 40 percent of its recent historical capacity, was once more than the republic’s largest inland sea. At one time it was Lake Jalisco, a massive body of water that not only covered most of this state, but substantial parts of adjoining regions.
Exactly how big it had been was the subject of educated conjecture and sheer fantasy for decades. Then, in the mid-1960s, a couple of North American Lakeside residents gave in to their curiosity and decided to try to corroborate their own speculations. Together with Mexican associates in Guadalajara, they began piecing together parts of Lake Chapala’s early physical history.
One of these Lakesiders was Ajijic’s late George Mitchell, a retired mining engineer with a trained geological turn of mind. Using topographical maps provided by the Guadalajara office of the Federal Department of Water Resources, Mitchell, Jesus Toscano of the University of Guadalajara, and their friends, found evidence of a gigantic Pleistocene body of water they quickly tagged “Lake Jalisco.” This immense sea not only covered the present day state of Jalisco, but parts of the states of Aguascalientes, Colima, Guanajuato and Michoacan.
It was a body of water almost beyond the imagination of those of us who live on the shores of today’s Lake Chapala. Lake Jalisco covered all of the geography from the city of Aguascalientes in the north, south to Ciudad Guzman and from Tequila in the west to Zamora in the east. The city of Guadalajara, all the towns along the lakes of Chapala and Atotonilco and today’s entire dry lake region of San Marcos, Zacualco and Sayula were mere lake bottom then.
Ice-Age Lake
To get a fix on just when all this water was here, one must slide back in time to those early freshman classes in Man & Civilization 101 and 102, and remember that the Pleistocene era was the great formative glacial period of prehistory that began between one and two million years ago. There were, scientists tell us, four worldwide advances of ice during this period, each separated by a thriving interglacial period. It was during this time that early man appeared. And it was in this period, probably just before the retreat of the latest glacial advance (about 36,000 B.C.) that Lake Jalisco was formed.
Before this last ice-age pushed southward, Jalisco is believed to have been much as it is today, for remains of pre-Pleistocene and Pleistocene era animals — mastodon, mammoth, pre-historic horse and camel, etcetera — have been found in the valleys and plains that were the Lake floor. Numerous habitation sites have been found on the edges and along the floors of these valleys, which obviously served as convenient routes for migrating pre-historic animals and perhaps even people both before the formation of Lake Jalisco and after its drainage.
Outlets
The absence of great salt deposits which would normally be expected at the site of so huge a lake (as a result of evaporation) suggested to investigators that Lake Jalisco had several drainage outlets. In searching for these outlets, they established that the near-maximum level of the Lake had been about 5,750 feet. Once this was determined (by the silt terraces and deposits left behind when the Lake subsided) the major drainage points became obvious — the Rio Tuxpan to the southwest and the Rio Santiago-Rio Verde to the north-east. Two other, not-immediately-apparent major outlets, the Rio Ameca and the Rio Ameria, were discovered while investigators were field-checking other, minor outlets.
Barrancas
Best estimates are that the original spill-over point for Lake Jalisco was a narrow arroyo to the north that parallels today’s Barranca de Oblatos, a part of the Rio Verde system. The Verde was then a young drainage channel flowing along a shallow barranca which the river has ruggedly notched to today’s depth, flowing into what is now known as the Rio Santiago which empties into the Pacific near San Blas, Nayarit.
The drainage at Rio Ameria (which leads to the Pacific Ocean near Tecoman, Colima) was punched through relatively late, when Lake Jalisco had reached is maximum level. The Rio Tuxpan over-flow point seems to have broken open much earlier near the present city of Tuxpan, beginning as a shallow barranca, eventually being cut deep and wide, the Lake’s water eroding out today’s young Tuxpan valley. Rio Ameca was the least important of these outlets, spilling over near La Higuera, and while cutting a good-size barranca, producing a swath of much less magnitude than either the Santiago or Tuxpan breakouts.
It is interesting to speculate what this vast inland sea must have looked like, shimmering from horizon to horizon, reflecting a pure and silent sky ... and what else? The peaks of the mountains that surround us today were islands then. And on these tips poking from this great sea were ... what? This was the time of small four-toed horses, giant armor-plated sloths and armadillo the size of elephants, mastodons weighing tons. The Ice-Age was also the season of early man’s appearance.
One can imagine him standing at the crest of Mount Garcia, a truly wild man, naked, watching the wind ripple his unnamed sea forever toward the horizon, a being without a known destiny or origin, simply there, silhouetted against a sky he had no word for, a silent, bodeful figure whose survival meant a step closer to the future of modern man.