You might have to do a few laps to get in some miles, but the loop around Virginia Lake is a pleasant, flat off-road run containing featuring some nice views. The trail is almost exactly 1 mile around the circumference.
The lake is 2 miles south of the center of Reno. For a longer run, one could take any number of roads to get there, in the easy-to-follow grid pattern of Reno. The trail is