var uri = new Uri("http://localhost:4567/Test/Callback#state=test&access_token=....");
// Contains the query
uri.Fragment
Results in:
#state=test&access_token=....
Edit:
To get the current url of website use:
Request.Url.AbsoluteUri;
In the Request.Url is all the information of the current page and in Request.UrlReffer everything from the previous page.
Note: Request.UrlReferrer is null when there is no previous request (from your website)