Remove email integration from calendar in mountain lion?
To Remove the Calendar completely. 

Go to the Mail, Contacts &amp; Calendars Preference in System Preferences select the google mail account and uncheck the Calendars &amp; Reminders



To Set the default Calendar for new events.

In Calendar the default calendar for new events is controlled in the Preferences.

You can set it to Selected Calender to make new events appear for the calendar you have selected 



or choose a  particular calendar