City girl in the mountains briefly exhausted racing across river (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

City girl in the mountains briefly exhausted racing across river ELBE (=river, in Germany) in [ HEID <i> (=girl in the mountains, in the novel by Johanna Spyri; “briefly” means last letter is dropped) + R <acin> G (“exhausted”, as in “emptied”, seems to imply dropping of all but first and last letters)