Partner joins old singer somewhere in California (4,4)
I believe the answer is:
'in california' is the definition.
('Palo Alto' is part of 'california')
'partner joins old singer' is the wordplay.
'partner' becomes 'pal' (pal can mean a friend).
'joins' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'singer' becomes 'alto' (alto is a kind of singer).
'somewhere' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for palo alto that I've seen before include "place in California", "city in California", "Californian city", "US city".)