Thunder River
... that the Grand Canyon's Thunder River is the steepest in the United States?
... that the Grand Canyon's <b id="mwAU8"><a class="mw-redirect" href="./Thunder_River_(Tapeats_Creek)" id="mwAVA" rel="mw:WikiLink" title="Thunder River (Tapeats Creek)">Thunder River</a></b> is the steepest in the United States?