From Highwire Press:
UC Press content is currently part of the Current Scholarship Collection at JSTOR. While UC Press will no longer include its current journal issues in this collection, its content will still available on, and form part of, the JSTOR archive collections.
The new UC Press HighWire platform will go live in mid-2015, but its current journal content will continue to be hosted on JSTOR throughout 2015 to facilitate a smooth transition for library customers. JSTOR will also continue to handle renewals for 2015.
Read the Complete Announcement
See Also: List of UC Press Journal Titles