Who was the architect that designed the first public library in
Altadena, California?  This building was probably built in the period
from 1920 to 1950.  When was it built?

Altadena's first public library was built in 1938, with the assistance
of federal WPA funding. The building was designed by Altadena native
Wallace Neff, one of California's most influential architects.
Altadena had a library previous to this, but the earlier library was
located in a school.

"[Altadena] has its own library district. Assessments voted on by
residents fund the libraries. The original main library building was
designed by architect Wallace Neff, grandson of Andrew McNally."

San Gabriel Valley Tribune: Altadena: Diverse population highlights foothill town
http://livinghere.sgvtribune.com/Stories/0,1413,281~28120~1411466,00.html

"1908

- Small school library established at Calaveras School, marks
beginning of an Altadena library district...

 1927...

- Altadena Library District established in accordance with State
approval. Mrs. Zane Grey elected first Board President...

 1938... 

- Lake Ave library built at corner of Beverly Way."

Altadena Town Council: Altadena History Timeline
http://altadenatowncouncil.org/altadenahistory/timeline.html

"In 1938, [William B. Davies] also secured WPA funding for the
Altadena Library Building on Lake Avenue. The library moved to its
present location on the corner of Mariposa and Santa Rosa, replacing
the Col. Greene mansion in 1968."

Wikipedia: Altadena, California
http://en.wikipedia.org/wiki/Altadena,_California

If you would like to learn more about Wallace Neff, these books may be of interest:

Amazon: Wallace Neff: Architect of California's Golden Age 
http://www.amazon.com/gp/product/0940512246

Amazon: Wallace Neff and the Grand Houses of the Golden State 
http://www.amazon.com/gp/product/1580931634

Amazon: Wallace Neff 1895-1982 The Romance of Regional Architecture
http://www.amazon.com/gp/product/0940512130

My Google search strategy:

Google Web Search: altadena architect "library building"
://www.google.com/search?hl=en&q=altadena+architect+%22library+building

Google Web Search: altadena "wallace neff" library
://www.google.com/search?hl=en&q=altadena+%22wallace+neff%22+library

I hope this is helpful. If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.

Best regards,
pinkfreud

Excellent job!

Thank you for the five stars and the nice tip!

~pinkfreud