Goat Trestle -- One of the best "bike walks"
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There is an improbable railroad trestle in Goat Canyon, that is more than worth checking out. A blurred photo is at http://www.roadtripamerica.com/places/deanza.htm
Also, Yuma isn't that far away and the Territorial prison is kinda fun: http://www.roadtripamerica.com/places/yuma.htm
The Desert View Tower is worth a drive, (if only because the ghost towns on old US-80 are so interesting). The tower is about 8 miles east of the Jacumba exit from I-8.
Felicity is home to another of the desert's odd characters and also to his vision of the "Center of the World" Pryamid.
One of my favorite road drives is Ocotillo northward on S-2 to CA-79 (check out the mistletoe on the trees around Oak Grove) and then past the wineries of the Temecula Valley. Some of the very best Calzones are made by the chef of the Temecula Pizza Company -- http://www.roadtripamerica.com/eats/temec1.htm