PRIOR TO DEPARTURE THE PILOT RECEIVED AN ABBREVIATED WX BRIEFING IN PERSON FROM THE RENO FSS, AND WAS GIVEN THE ADVERSE WX CONDITIONS & CURRENT WX FOR HIS PLANNED ROUTE OF FLIGHT. HE WAS ALSO ADVISED THAT VFR FLIGHT WAS NOT RECOMMENDED. THE AIRPLANE WAS LATER OBSERVED FLYING OVER A HIGHWAY AT LOW ALTITUDE; WHICH THE WITNESSES DEFINED AS NOT HIGH ENOUGH TO CLEAR A MOUNTAIN RIDGE. THE TOP OF THE RIDGE LINE WAS OBSCURED, & THE AIRPLANE WAS IN & OUT OF THE BOTTOM OF THE CLOUDS. THERE WERE ALSO RAINSHOWERS IN THE AREA. THE RIGHT SEAT PILOT ALSO HELD AN ATP CERTIFICATE. HE WAS BEING TREATED FOR GLAUCOMA & WAS TAKING THE PRESCRIPTION DRUG ISOPTO CARPINE (PILOCARPINE). THE DANGER OF ADVERSE REACTIONS OR SIDE EFFECTS OF THE DRUG INCREASES WITH THE USE OF ALCOHOL. THESE EFFECTS INCLUDE REDUCED VISUAL ACUITY. THE RIGHT SEAT PILOT WAS WITH A GROUP THAT REPORTED HAD A FEW COCKTAILS THE NIGHT BEFORE THE ACCIDENT.