Is there a way I can access my C drive? I am a Windows Phone developer and I need to transffer some files that are created on the Local State (In Windows 10 desktop, this would be in C:\Users(UserName)\AppData\Local\Packages(App ID)\LocalState). There is a trick online about using a Windows Desktop shortcut file as well as using the File Explorer URL bar to access C but none of these work on the latest version of Windows 10 Mobile.
You can use the Windows Phone Power Tools to access the isolated storage of apps that you've deployed to the connected device as a developer (so not apps that you've installed through the store)
In addition to what Rowland Shaw said, it should be quite easy to just copy them programmatically to a folder that you can access (e.g. Music). I haven't tested this, but off the top of my head I think it would be something like:
await (await ApplicationData.Current.LocalFolder.GetFileAsync("MyFileName")).CopyAsync(KnownFolders.MusicLibrary);