The tradition is a carryover from 1825 and 1834, when Guam’s faithful made a "promesa" (promise) to hold a procession in Mary’s honor after a series of devastating earthquakes.
Exquisite image of Our Lady, with hands, feet and face of ivory and a cap of natural hair, is bedecked with a jewel-studded crown of gold and gold jewelry. For centuries, Chamorros have held this visual image of the Immaculate Virgin which has survived fires, earthquakes, and typhoons. She was safely hidden from the Japanese invaders and otherwise protected from the ravages of World War II.
Government Code of Guam Sect.1 Chapt 10 paragraph 1000 designates Our Lady of Camarin Day as an official holiday on December 8th. Since the early 1900s, on that Feast day, the Basilica is closed, the statue is taken down from the apse, groomed by a select group of people, and is placed atop a karosa or cart of blossoms. The cart is pulled with the centuries old carved figure being a central visual image leading a Catholic procession around Hagatna, the capitol city of Guam. Throughout the procession, the sound of prayers in various languages weave through the thousands of faithful believers honoring Jesus through Mary who is identified as the Immaculate Conception. As with religious traditions in the Marianas, Catholics do not pray to statues or do not worship statues.
Source: ns.gov.gu