[AndrewF]

#6 THWN hot conductors, with a #10 ground satisfies the Code for a 60 Amp feeder. You could even use a smaller neutral conductor (#8) if you wanted to. Plenty of room in that 1¼ conduit.

This is what I would do. I wouldn't use URD and then have two splices in the line.

How big is your structure? You sure 60 amp is big enough for say a welder, power tools, air-compressor, etc?

I ran 100 amp to mine, and now have about 80' of #2 left over.

http://www.diychatroom.com/f18/running-service-barn-100-amp-45915/