From 1906-1967 (the start date is up for debate), seaside towns were known to use the coastline as dumps, Fort Bragg was no different. After the devastation of the San Francisco earthquake the streets were filled with rubble and trash was dumped on the coast for the ocean to wash away. This of course, included plenty of glass.
It wasn’t until 1967 when city leaders and the North Coast Water Quality Board realized what a mistake it was and sought to relocate the dump away from the ocean and clean up the shoreline. After the clean-up and more decades of crashing ocean waves; only smoothed and rounded glass mostly remained.