to power trains, cars and trucks
N is for noxious)
The high Sierra Nevadas can't always be seen through the dense haze, the magnificent snow capped peaks are hidden, yet you know they're there ... somewhere.
From the valley floor, you drive through mile upon mile of orange groves, the sprays and fertilisers adding to the toxic potion rising up into the mountains when the conditions are right (or wrong depending on how you look at it).
The geography and climate cause an inversion layer to form over the valleys, trapping the air and concentrating the pollutants in it. A high proportion (10%) of the US population lives in California, and whilst air quality has improved over the years, more will need to be done to ensure the survival and health of the plants and animals in the surrounding peaks as well as the health of the people on the valley floor.
A 2013 interactive map by the California Environmental Protection Agency showing assorted data including pollutants can be found via this link.