No one in Colfax or Auburn will breathe a whit easier knowing this, but the heavy wildfire smoke that gave their towns a carbon black eye on the Air Quality Index on Monday is historically the norm for the foothills, studies show.

Analysis of tree rings and oral histories of American Indians and Euro-American surveyors suggests that the cobalt blue skies typifying the Sierra today were more the exception up through the 19th century.

The skies likely were smoky much of the summer and fall in the mountains and other remote and parched regions of California, where fires were largely ignored.

The Chumash Indian name for what is now the Los Angeles area translates to "the valley of smoke," according to Gordon J. MacDonald, a geophysicist and professor formerly with the University of California, San Diego.

The chronic pall of dense smoke frustrated mapmakers. As C.H. Merriam, chief of the federal Division of Biological Survey, noted in 1898:

"Of the hundreds of pers