"You've been out here countless times. Does it still have an impact?" CBS News correspondent Seth Doane asked Bill Toone, the founder of the Ecolife Foundation.
"Absolutely, I stood in this forest the other day filming and I started to cry - and that's after 23 years," Toone said.
For Toone, a veteran conservationist, this site is both awesome and troubling.
There are an estimated 250 million monarchs that winter in this preserve. That sounds like a lot - and it certainly looks like a lot, but imagine 15 years ago when there were nearly one billion. The problem is giant fir trees where monarchs huddle for warmth are being cut down.
Without cover, millions of butterflies often freeze to death - in an average year, up to 15 percent. But this year, bad weather killed more than 50 percent.
Right now, we're inside a protected area of about 140,000 acres that the Mexican government set aside as a preserve for the monarch butterflies. Still, inside this zone, every year, more than 100,000 trees are cut down.
Mexico recently lost nearly 7 percent of its forests, an area twice the size of New Jersey, much of it from illegal logging. Deforestation threatens more than butterflies, as it destroys watersheds which can cause mudslides. One five miles from a butterfly sanctuary killed 17 people.
But even average families contribute to the problem, consuming about 40 trees a year to cook and heat their homes.
Son Toone's group Ecolife now builds and donates fuel-efficient stoves here in the Mexican state of Michoacán, reducing a family's wood consumption up to 75 percent, to just 14 trees a year.
Toone said the secretary of the environment in Mexico would love to see 600,000 of these stoves in Michoacán, and they've built 500 so far.
"Our work is cut out for us," Toone said.
Ecolife is also pledging to plant a million new trees over the next three years.
Now, the monarchs are leaving these forests, mating along the way. Over summer, four generations will be born and die, each living about a month before a "super generation" arrives. They'll live seven months, and having never been to Mexico, will somehow find their way, back to these same ancient forests.
Dr. Lincoln Brower, the world's leading monarch expert said this magnificent migration is definitely worth saving.
"How would the world be different without the migration of the monarch butterfly?" Doane asked.
"My answer to that is - what good is the Mona Lisa? What good is Mozart's music? We could live without it, but we would be diminished as a culture and as a people," Brower said. "There is nothing like it. It is unique."
But saving the migration means saving the forest. The question is: How much time do these monarchs really have?