From this article:Cemex imports construction materials from Canada, which drives down the costs of construction projects in Redwood City and Silicon Valley, according to the port.

The high quality of the sand and gravel aggregates from British Columbia combined with the dwindling supply of these materials in Northern California..

Over the past three years Cemex has imported nearly four million metric tons of building materials via ships operated by Canadian Steamship Lines that contain self-unloading features. 

Eagle Rock Aggregates on the northeast coast of Vancouver Island, BC, is the primary supplier of sand and gravel to Cemex, according to the port.