A320 FLC HAD TCASII TA AFTER ENCOUNTERING SEVERE CLR AIR TURB OVER THE ROCKY MOUNTAIN FRONT RANGE. FLT ATTENDANT AND PAX INJURIES RESULTED.

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ACR X FLT JFK TO LAS. WE WERE AT CRUISE PHASE OF FLT AT FL310 APCHING THE FRONT RANGE OF THE COLORADO ROCKIES. WE HAD HEARD RPTS OF MOUNTAIN WAVE ASSOCIATED TURB AT HIGHER ALTS; SO WE NOTIFIED THE FLT ATTENDANTS; TURNED THE 'FASTEN SEATBELT' SIGN ON; AND MADE A PA ANNOUNCEMENT FOR THE PAX TO REMAIN SEATED AS A PRECAUTIONARY MEASURE ALTHOUGH THE FLT WAS SMOOTH; SINCE THERE HAD BEEN RPTS OF TURB IN THE AREA. APPROX 3-4 MINS LATER; WE WENT FROM SMOOTH AIR TO AN ABRUPT ENCOUNTER OF SEVERE TURB WHICH LASTED BTWN 7-10 SECONDS. THIS ENCOUNTER CAUSED THE ACFT TO DROP IMMEDIATELY 400 FT LOWER IN ALT. THE AUTOPLT DISCONNECTED AND THE ACFT ATTITUDE PITCHED DOWN. THE FO RECOVERED THE ACFT TO A STABLE ATTITUDE AND BACK TO FL310. WE NOTIFIED ZDV AND REQUESTED FL280 TO FIND SMOOTH AIR. 2 FLT ATTENDANTS RPTED MINOR ANKLE INJURY AND A FEW PAX RPTED SOME NECK AND BACK SORENESS. WE CONTACTED OUR DISPATCH AND CONTINUED TO LAS WITH NORMAL FLT CONDITIONS FOR THE REMAINDER OF THE FLT WHERE PARAMEDICS MET US AT THE GATE UPON OUR ARR. OUR COMPANY DISPATCH HAD CONTACTED US ABOUT 30 MINS PRIOR WHICH ALERTED US TO TAKE PRECAUTIONARY MEASURES BEFORE ENCOUNTERING THE CLR AIR TURB. SUPPLEMENTAL INFO FROM ACN 508691: AUTOPLT DISCONNECTED AND ACFT ATTITUDE WAS UPSET. WE RECOVERED ACFT ATTITUDE AND CLBED BACK TO FL310 AND NOTIFIED ZDV AND REQUESTED FL280. FROM THE TCASII WE DID RECEIVE A TA. WE ALSO ADVISED ATC ABOUT THE TA THAT WE RECEIVED WHILE IN THE TURB. WE WERE AT ONE OF THE BETTER ALTS ACCORDING TO ZDV; BUT THE TURB WAS A LOT WORSE THAN EXPECTED. ONE FLT ATTENDANT HAD A BROKEN ANKLE AND ANOTHER WITH A SPRAINED ANKLE AS WELL AS ABOUT 3-4 PAX THAT WERE TREATED AND RELEASED FROM A LCL LAS VEGAS HOSPITAL. AFTER RECOVERING THE ACFT FROM THE UPSET DUE TO THE TURB; WE CALLED THE FLT ATTENDANTS TO DETERMINE THE DAMAGE AND ANY INJURIES. WE DETERMINED WE HAD MEDICAL HELP ON BOARD AND WITH NO LIFE THREATENING INJURIES WE CONTINUED TO LAS WHERE WE WERE MET BY EMER PERSONNEL.