One of the best features that SP1 brought to SharePoint administration is the ability to recover deleted site collections. I’ve had many incidents where this came handy.
You have to use PowerShell or Object Model recover a deleted site collection. Here is how you can do it using PowerShell.
In SharePoint 2010 Management Shell, provide the following command.
Restore-SPDeletedSite -Identity <relative URL or GUID>
More details on this command can be found in this Technet article. The deleted site collections are stored as SPDeletedSite objects. If you do not remember the URL or GUID of the deleted site collection, you can find it using the command,