C172 ENCOUNTERED WAKE TURB FROM B737 AFTER IT PASSED 1000 FT OVERHEAD ON THE SAME COURSE.

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HAD DEPARTED PAO ON AN IFR FLT. AFTER AN UNEVENTFUL VECTORS DEP; WE WERE CLRED TO JOIN; AND PROCEED VIA OUR FILED RTE. WE WERE ESTABLISHED AT 6000 FT MSL; ON A NORTHERLY HEADING. ABOUT 20 NM W-SW OF SACRAMENTO; WE WERE ADVISED THAT A B737 (BELONGING TO A 121 OPERATOR) WOULD FLY 1000 FT OVER US; SAME HDG. WE LOOKED FOR THEM; AND A FEW SECONDS LATER; THEY APPEAR 12 O'CLOCK; DIRECTLY OVER US. WE TOOK PRECAUTIONS FOR A WAKE ENCOUNTER; SINCE WE WERE ON THE SAME HDG; AND WAKE TENDS TO SINK. WE WAITED FOR APPROX 2 MINS; AND NOTHING HAPPENED. BY THIS TIME THE ACFT WAS VERY FAR (PROBABLY 8-10 NM) 12 O'CLOCK; AND WE CONSIDERED IT TO BE NO LONGER A FACTOR. JUST AS WE LOWERED OUR GUARD; THERE WAS A 30 DEG ROLL TO THE R; FOLLOWED IMMEDIATELY BY A VIOLENT L ROLL TENDENCY. AT THIS POINT OUR ACFT HAD ENTERED A 90 DEG L ROLL; AND THE NOSE STARTED TO DROP. THE PF; FOLLOWED NORMAL UNUSUAL ATTITUDE RECOVERY PROCS; AND WE RETURNED TO LEVEL FLT WITH ONLY A 50 FOOT ALTITUDE LOSS. IT TOOK US SEVERAL MINS TO REALIZE WHAT HAD JUST OCCURRED; AFTER THINKING OF EVERY POSSIBLE CAUSE FOR THE EVENT. AT NO POINT WERE WE ISSUED A WAKE TURBULENCE WARNING (ONLY A TFC WARNING). IT MAY BE A GOOD IDEA TO MAKE SURE CTLRS ARE AWARE OF WAKE TURBULENCE RISKS EVEN WHEN NOT IN LNDG-TAKEOFF OPS; PARTICULARLY; WHEN 2 ACFT OF SUBSTANTIALLY DIFFERENT SIZE/WEIGHT ARE INVOLVED; AND ISSUE CORRESPONDING ALERTS; OR BETTER YET; TAKE PREVENTIVE MEASURES; SUCH AS AVOIDING HAVING A HEAVY ACFT FLY 1000 FOOT ABOVE A LIGHT ACFT; WHEN ON THE SAME HDG AND COURSE LINE.