ZDV CTLR INADVERTENTLY TERMINATED IFR SERVICE THINKING THE ACFT WAS VFR; CLAIMING FATIGUE AS CONTRIBUTING FACTOR.

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I WAS WORKING SECTOR 36/68 RADAR BY MYSELF; ON POS FOR OVER AN HR. THIS IS A LARGE LOW ALT SECTOR (GND TO FL260) WITH UNCTLED AIRSPACE; ESPECIALLY N AZ/S UT. I HAD STRUGGLED WITH TA'S IN THE FMN AREA WITH 6-8 VFR LIMITED TARGETS WITHIN 5 MI OF FMN CONSTANTLY. THE TFC IN THIS SECTOR TENDS TO CONCENTRATE IN THE FMN/DRO AREA WITH FAR LESS VOLUME AROUND TBC/PGA. A CDC RADAR OUTAGE WAS AFFECTING THE TBC/PGA AREA AND I HAD EARLIER CANCELED SEVERAL VFR FLT FOLLOWING PLANS BECAUSE I COULD NOT PROVIDE RA'S IN THIS AREA. ZLA08 HANDED OFF ACFT X E OF GCN ON V108 AT 110. ZDV NEVER HAS RADAR COVERAGE LOW IN THIS AREA W OF TBC SO I SAW THIS HDOF IN COAST TRACK. ZLA08 HAD NOT CALLED WITH A NON-RADAR APPREQ (NORMAL PROC FOR AN IFR IN COAST TRACK) SO I ACCEPTED THE HDOF; THINKING THE ACFT WAS VFR. EVEN AFTER I CHKED THE RTE; GCN V108 HVE CNY (ODD FOR A VFR TO FILE A RTE SO NON-DIRECT); I STILL REMAINED CONVINCED THE ACFT WAS VFR. ACFT X CHKED ON AND I ADVISED THE PLT I WOULD NOT BE ABLE TO PROVIDE RA'S; TERMINATED FLT FOLLOWING AND TOLD HIM TO SQUAWK VFR. THE PLT ACKNOWLEDGED. ZLA08 CALLED IN A FEW MINS TO ASK IF ACFT X HAD SQUAWKED VFR AND I ADVISED I HAD TERMINATED FLT FOLLOWING. I THEN ASKED ZLA08 IF THEY ALWAYS HAD RADAR IN THIS AREA; I WAS SURPRISED ZLA08 HAD SEEN THE CODE CHANGE; AND WERE THEY NOT AFFECTED BY THE CDC RADAR OUTAGE. THE ZLA08 CTLR SAID THEY DID HAVE RADAR AND WERE NOT AFFECTED BY THE OUTAGE. A FEW MINS LATER; MY FLM CAME OVER BECAUSE HE HAD BEEN CALLED BY ZLA WONDERING WHY I HAD TERMINATED AN IFR FLT PLAN. I NOW BEGAN TO REALIZE MY MISTAKE AND FORTUNATELY HAD SUGGESTED THE PLT MONITOR MY FREQ; SO I CONTACTED ACFT X AND APOLOGIZED AND ATTEMPTED TO REENTER HIS FLT PLAN AND CLR HIM IFR AGAIN. I ADVISED THE PLT HE WOULD HAVE TO CLB TO 140 TO FLY V108 NE OF PGA (140 MEA). THE PLT SAID HE COULD NOT CLB SO I NOW TRIED TO WORK OUT A NON-RADAR RTE THAT WOULD ALLOW HIM TO STAY AT 110 AND CONTINUE ON A DIRECT COURSE TO CNY. THIS IS IMPOSSIBLE DUE TO BOTH NAVAID LIMITATION AT LOW ALT AND THAT OFF V108; THAT AREA IS UNCTLED BELOW 145. I EXPLAINED THIS TO THE PLT AND HE DECIDED TO CONTINUE VFR WITH NO ADVISORIES AND JUST MONITOR MY FREQ. THIS SITUATION WAS CAUSED BY SEVERAL FACTORS BUT THE MAIN ONE WAS PROBABLY FATIGUE; BOTH TIME ON POS AND CUMULATIVE FROM MY 2-2-1 REVERSE ROTATION SCHEDULE. I WAS UNAWARE THAT ZLA08 HAD RADAR COVERAGE LOW E OF GCN AND ZDV36 DOES NOT AND WONDER IF ZLA08 KNOWS I AM SEEING A COAST TRACK? I WILL PURSUE THIS AND INCREASE MY VIGILANCE WHEN I AM FEELING FATIGUE.