Every November some trees in Pacific Grove are a magnet for Monarch butterflies.
"Many people walk by them and don't see them because they think they are dead leaves," said butterfly docent Jim Beigle.
One location is called an over wintering site. Mild conditions from November to February attract the butterflies from as far as Southern British Columbia -- more than 1,000 miles away.
When the Monarchs come, so do the people.
"It was just awesome I've never seen so many butterflies ever in my life," said sanctuary visitor Keri Birgl.
This year there's an estimated 15,000 butterflies literally hanging out for the winter.
Pacific Grove is so passionate and protective of its Monarchs that in 1990 the city bought a 2.4 acre grove and made it a sanctuary.
This is the third year city leaders have given Jessica Griffiths from Project Monarch Alert a special permit to net and tag the Monarchs.
"We want to understand the best way to protect the monarch butterfly so we need to know how many over wintering sites there's using, where they're going and how far they move," said Griffiths.
About 3,000 butterflies become a number.
"This tag does not harm the butterfly in any way it's not heavy, it does not impede its flight in any manner," said Griffiths.
Previous taggings reveal the Monarchs move around flying as far as 60 miles to another wintering site. There are about 300 west of the Rockies. The annual migration is a source of wonder.
"That they are able to figure out to land on this particular spot on this huge earth, it's quite amazing," said San Francisco tourist Albert Lin.
The Monarchs are just as intuitive about the timing of their departure.
"They will be here until February and then for some reason they know the milkweed has come out of the ground," said butterfly docent Donald Slaiter.
When the butterflies leave, Pacific Grove still has its breathtaking coastline and famous Victorians, but the city is most proud of its winter guests and efforts to protect its habitat.