It was originally the route of the Southern Pacific Railroad, now long since gone; although traces remain in Walnut Creek, where the train depot is now a steak restaurant; and in Danville, where the moved depot is now the Museum of the San Ramon Valley. (It's also the route of a petroleum pipeline — not unusual alongside railroads, as train routes are continuous, flat, and otherwise unused — which caused a nasty explosion in Walnut Creek last year.)
Its origin as a railway makes for a flat, easy-to-walk trail, largely flanked by trees and homes. Sometimes a bit too flat and a bit too dull: views are often limited.
We walked from Danville to Alamo and back; about 3 miles each way. Park in the Museum/Andronicos lot in Danville (4 hours parking weekdays/Saturday; unlimited Sunday).
Ice-cream at Rite Aid makes a good reward at Alamo. Not only does Rite Aid (a drug store) have its own ice cream brand ("Thrifty", a legacy of its acquisition of the Thrifty chain in 1996), but: (a) it's good, (b) it's cheap, and (c) some Rite Aids, including the Alamo one, have an ice cream counter. Very odd; it's like popping into Boots for corn plasters and a vanilla cone.
(For future reference: pistachio, caramel pecan, choc chip, mint choc chip, and chocolate malted crunch are good. Coconut and pineapple sounds wierd but is good. Black cherry is disappointing: not cherry-ey enough. Cups cost the same as cones, but seem to get a more generous scoop.)
We walked back into Danville just as dusk was falling: lots of frog croaks to be heard. But we almost left it too late: the trail isn't lit and isn't much fun in the dark.