Ah.
Up and Down California in 1860-1864;
The Journal of William H. Brewer
I read this this year, and it is an amazing book about the discovery of all of California Terrain, including the Sierra.
out of print, but available. Highest Recommendation, virtually unknown
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The Last Season by Eric Blehm
Much discussed book, very well received and factual, about the current Sierra, in the area in which you will be hiking.
Highest Recommendation, in print
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Mountaineering in the Sierra Nevada (High Sierra Classics Series) by Clarence King
A quaintly written book that includes the discovery of Whitney!