Himachal Pradesh trounced Assam by an innings and 221 run after the visiting batsmen collapsed miserably on the third and penultimate day of their Group C Ranji Trophy encounter in Dharamsala today.After amassing a mammoth 463 for nine in their first innings in response to Assam's paltry 81 all out, Himachal bowled out the visiting side for 161 to record the huge win.