A C172 INSTRUCTOR AND STUDENT LANDED ON A CLOSED RWY AT ELN.

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MY STUDENT AND I WENT ON A XCOUNTRY FLT FROM OUR LCL ARPT TO ELN; WA. PRIOR TO DEPARTING; I RECEIVED A THOROUGH BRIEFING FROM THE LCL FSS. THE ONLY NOTAM THAT WAS MENTIONED WAS AN UNLIGHTED TWR. ABOUT 20 MI FROM THE ELN ARPT; WE TUNED INTO THE ASOS. THE WIND WAS VARIABLE AT 4 KTS. I CHKED THE 'FLT GUIDE' AND SAW THAT THE PREFERRED RWY WITH WINDS UNDER 5 KTS IS RWY 7. WE HAD BEEN MONITORING THE CTAF FOR 10-15 MINS AND THERE WAS NO RPTED TFC; AND WE WERE COMING OFF OF THE V2 AIRWAY; AND WE WERE LINED UP STRAIGHT-IN FOR RWY 7. WE ANNOUNCED A 5 MI STRAIGHT-IN FINAL AND A 3 MI FINAL FOR RWY 7. WE TAXIED FOR TKOF TO THE XING RWY 29. AFTER ANNOUNCING 'TAKING OFF RWY 29; STRAIGHT OUT DEP;' WE WERE INFORMED BY UNICOM THAT WE HAD JUST LANDED ON A CLOSED RWY (RWY 7). AFTER TKOF AND CLBING TO A SAFE ALT; WE CIRCLED AND FLEW ALONG THE ENTIRE LENGTH OF RWY 7/25 TO CONFIRM THAT THERE WAS NOT A YELLOW X PAINTED ON THE RWY; AND THERE WAS NOT! WE INFORMED UNICOM THAT WE HAD NOT SEEN ANY NOTAMS PERTAINING TO A CLOSED RWY; NOR ANY X'S ON THE RWY. AFTER LNDG; I CONSULTED THE AFD AND SAW THAT; LISTED IN THE REMARKS SECTION AT ELN; RWY 7/25 IS CLOSED. I GUESS I LEARNED A LESSON: CONSULT THE AFD PRIOR TO LNDG AT ANY UNFAMILIAR ARPT. BUT WHY WERE THERE NOT ANY X'S ON THE CLOSED RWY? EVEN A TEMPORARY ONE? AND WHY WERE THERE NOT ANY NOTAMS OUT FOR THIS? ANY WHY WASN'T THERE ANY NOTICE PUT ON THE ASOS WARNING OF THE CLOSED RWY? I'VE HEARD SIMILAR NOTICES ON OTHER ASOS'S. AND; BETTER YET; WHY DIDN'T UNICOM INFORM ME OF THE CLOSED RWY AFTER I ANNOUNCED FINAL FOR RWY 7? TWICE?