Emigrant can be one of the first trails to shed the winter snow, so it makes a good early season warm-up. It's also a great longer ride that beginners and intermediates can tackle.
There are several options to start this ride, many folks will start at the Donner Party Picnic Area (insert joke here) off the 89 just north of Truckee. Options exist to start off Alder Creek Rd or where the trail crosses Shussing Way for some fun technical challenges (bridge crossings) before crossing Alder Creek then the 89 to get to the Donner Area parking lot.
From here the singletrack starts off paralleling the north side of Prosser Creek and heads back towards the 89. Late in the season you may be able to cross Prosser Creek, but it's best to ride to the 89 and over a short bridge. Then you'll parallel the south side of the creek and soon turn uphill to cross a dirt road. Follow the singletrack all the way to Stampede Reservoir. Along the way you'll cross a number of dirt roads, but the main crossings are marked and the way across the minor ones are pretty obvious.
This is typically an out-and-back ride, all singletrack, with great meadow and long distance views. Although there are no prolonged climbs, there are no prolonged descents. You'll feel a great burn regardless of your ability, which should dictate your turn-around point.