You may wish to produce events on more than one calendar from data contained in the same Sheet of Event Information in your Google Spreadsheet. This will require you designate a column in the Sheet that will hold the Calendar ID.
Calendar IDs for primary calendars are simply the email address of the user.
Calendar IDs for secondary calendars can be retrieved from Calendar Settings (see below)
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Once you have identified and populated the calendar IDs in your Sheet of Event Information select the Merge to Multiple Calendars checkbox (available if advanced features are enabled) and select the calendar ID column.