I was pulled over immediately prior to the 35 m.p.h. speed limit sign entering the City of Elsberry southbound. The speed limit on Highway 79 (between several small towns) is 60 m.p.h. The speed limit drops to 30 or 35 as you approach these small towns. I was pulled over before the 35 m.p.h. speed limit sign as you enter Elsberry going south. Before entering Elsberry there is nothing but river road and bluffs. I was casually driving 52 m.p.h. thinking the speed limit was 60 m.p.h. Somewhere prior to the 35 m.p.h. sign and for no good reason, they had dropped the speed limit to 40 m.p.h. Neither of my two passengers saw this sign. There were no notices stating an upcoming reduction in the speed limit. I noticed (after receiving the ticket) as I drove past the 35 m.p.h. sign, there was another speed limit sign within a couple hundred feet dropping it to 30 m.p.h. As I drove out of town, there was another speed trap on the east side. The police car was hiding on a small dirt lane hidden by tall weeds and brush.