NMAC. SEE AND AVOID. ACFT DSNDING AND VFR ACFT WITH NO XPONDER.

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THE FLC CANCELED IFR DSNDING THROUGH 10000 FT REMAINING WITH ZLA ON SAME MODE C CODE FOR TA'S. THE IPL ARPT WAS CLRLY IN SIGHT. THE DSCNT RATE WAS STABILIZED AT 210 KIAS; 1500 FPM AS PER COMPANY DSCNT PROFILE. THE FLC WAS ACTIVELY SCANNING THE AREA FOR TFC; ESPECIALLY DUE TO R- 2510B BEING ACTIVE WITH UNITED STATES NAVY JET ACFT OPS. SCANNING (FO; PF) 12:30 O'CLOCK POS TOWARD THE 3 O'CLOCK POS; LEVEL; A HIGH WING CESSNA OBSCURED ALL VIEW. NO REACTION TIME AVAILABLE. THE CESSNA APPEARED TO BE FLYING WBOUND AT 8500 FT DIRECTLY ON V458; THE HEAD-ON ACFT DID BEGIN AN EVASIVE PULL-UP AND L TURN TOWARD THE SW. VERY CLOSE. 50 FT VERT; 50 FT HORIZ; 20 NM W IPL; 8500 FT MSL. THE PNF; SCANNING 11 O'CLOCK POS TOWARD THE 9 O'CLOCK POS; SNAPPED HIS ATTN TOWARD THE FO'S STATION UPON HEARING EXPLETIVE FROM THE FO. THE FLC BECAME VISIBLY SHAKEN. FO IMMEDIATELY QUERIED ZLA ABOUT ANY TARGETS IN OUR AREA; IF ANY AND PARTICULARLY ANY BEHIND OUR POS WBOUND. ZLA RESPONDED THEY DISPLAYED NO OTHER TARGETS IN THAT SECTOR EXCEPT FOR US. THE FLT CONTINUED TO ITS DEST CANCELING RADAR SVCS PRIOR TO ENTERING THE NON CTLED IPL TFC PATTERN. COMMENT: IN AVOIDING FLT INTO MEXICAN AIRSPACE; MANY VFR FLTS TEND TO FLY V458 FOR NAV GUIDANCE. IT APPEARS OUR NEAR MISS WAS DUE TO HIGH CLOSURE RATE; HIGH RELATIVE DSCNT RATE AND THE FACT THAT THE CESSNA'S XPONDER WAS TURNED OFF OR INOP. IN ADDITION; THE CESSNA WAS FLYING INTO A LOW AFTERNOON SUN; OBSCURING THE VIEW OF OUR ACFT TO HIS OPPOSING ACFT. THIS AIRSPACE CORRIDOR BTWN R-2510B AND THE MEXICAN BORDER DESERVES TO BE REVIEWED FOR PERHAPS ADVISORY CIRCULAR INFO TO BE DISSEMINATED TO ALL PLTS IN THIS REGION. CHK YOUR XPONDERS AND MODE C CAPABILITIES. VIGILANCE; OF COURSE; BUT BLIND SPOTS CAN OCCUR. VFR PLTS; ATTEMPT TO RECEIVE VFR FLT FOLLOWING AND TA'S; USE ALL AVAILABLE RESOURCES - - BE SEEN!