Mt. Garcia. El cerro de Garcia

When did it last erupt??

Probably several million years ago.

Wonder where I could research it. Google no help.

sm1mex wrote:Wonder where I could research it. Google no help.

Try contacting the Department of Volcanology, Institute of Geofisics, UNAM Cd de Mexico.
They probably have a lot of info and/or, could direct you to research material.
Any geology studies program at any Universidad in Mexico might have research sources of info.

I highly recommend reviewing this website: https://geo-mexico.com/ and the locally written book: https://www.amazon.com/Geo-Mexico-geography-dynamics-modern-Mexico/dp/0973519134 Tony Burton is a treasure of an author and a scholar.

Thomas Hellyer - Thanks for such kind words; they are very much appreciated.
There is no evidence, to my knowledge, that Mt. García has erupted in post-Conquest times. On the other hand, it still has a well-defined crater, so my best guess would be that it last erupted sometime in the past million years, but not in the past 600! When I get chance, I'll reread some of the geological papers I have stashed away somewhere and report back if I find anything that narrows down or refutes that very broad time frame. The fault system that created the graben/rift valley that the lake occupies is believed to date back about 12 million years.

Below is a link to a research paper from 1995 that discusses the dating of volcanic rock samples collected from 42 sites surrounding the Chapala Region.  The paper states:

"The reversed polarity of Cerro García Formation was assigned to the Matuyama Chron (a period of time ranging from about 1 to 2-1/2 million years ago) based on the geomorphology of the volcano and in accordance with a K-Ar age of 1.7 Ma (1.7 million years)."  

Perhaps someone with a knowledge of geology could have a look and tell us what this means in terms of when Cerro García may have last erupted.

= = = = = = = = = =

Southwestward volcanic migration in the western Trans-Mexican Volcanic Belt during the last 2 Ma
Hugo Delgado Granados, et al.
Geofísica Internacional, January 1995
bit.ly 33sDN59

cerebrozo, Thanks! That is one of the articles I was going to look for. The article suggests that my 1 million guesstimate is the lower end of the age range for Cerro García as a volcano. As you realize, that does not, however, necessarily indicate when the volcano last erupted. My background is actually in geomorphology. Cerro García still has a relatively well-defined crater, which time will eventually obliterate. By comparing it to volcanoes elsewhere in Mexico, where the chronology is much better established, I would guess that Cerro García has not erupted in the last 100,000 years or so. If I find out more when I have chance to dig out other relevant papers, I'll report back.

Janice Edith wrote:Probably several million years ago.

As cerebrozo said, 1 to 2 1/2 million years is probably the time frame.  I don´t think the OP is going to get an actual year for whatever research they are doing.