Sentence:  Along the base of the Sierra, back of Pasadena, on eastward back of San Gabriel, past Cucamongo, with its noted vineyards, above Pomona and on beyond San Bernardino, growing warmer as it recedes eastward from the sea, is a belt of foothills above the <WSD>fog line</WSD>, facing out toward the noonday sun, looking down across the plains and the hills of the Coast Range upon the warm, southern sea, and yet fanned daily by an ocean breeze that has no harshness. 
Meaning of the word marked with <WSD> tags:  A division in (altitude) above which (fog) appears.