Keep your head on a swivel out there... I was returning from a long (8000 mile) trip and made a stop at U42 (South Valley Regional, south of SLC and under the Bravo). I had come from the east and turned south over the valley (remaining east of the Bravo) to descend. Runway 34 was in use with a left pattern. Once I was below the Bravo, I asked for a frequency change and went to CTAF. I called 5 miles, 3 miles, 1 mile and stated my intentions. I flew perpendicular to the runway, approaching from the east, directly toward the 16 numbers at pattern altitude. When I was about a mile away (still on the east side of the runway), another plane (also talking on CTAF), took off and remained in the pattern. I watched him turn crosswind and said I would follow him. Spacing was good and everything looked great. At about 3/4 mile from the runway (still on the east side), without having spoken on the radio, a 172 flies about 200-300' above me and maybe 1/4 mile in front of me, going diagonally (aiming for the point where one would turn from downwind to base). After passing me, she called to say that she "had the Dakota behind me". She was not in position to enter the pattern and ended up continuing west to sort things out and reenter the pattern. She sounded like a student pilot solo. It sure surprised me. Neither my wife (who is excellent at spotting traffic) nor I had seen her. I had never been to U42 but it seems to be a busy airport under the Bravo and I think a tower would have prevented this sort of thing. I don't think it was close enough to call it a near-miss, but it was still too close for comfort. Looking at AirNav, U42 has 208 operations per day. FCM (Flying Cloud) also has 208 operations per day and is similarly positioned under the Minneapolis Bravo. FCM has a tower.