Retrieve stored TIMESTAMP values in a particular time zone

This is really easy. All TIMESTAMP values are stored in universal time, and always converted to the present time_zone setting whenever they are rendered.

SET SESSION time_zone='America/Los_Angeles'; 
SELECT timestamp_sold
  FROM sales
 WHERE state_sold = 'CA'

Why is this? TIMESTAMP values are based on the venerable UNIX time_t data type. Those UNIX timestamps are stored as a number of seconds since 1970-01-01 00:00:00 UTC.

Notice TIMESTAMP values are stored in universal time. DATE and DATETIME values are stored in whatever local time was in effect when they were stored.