(Portland, OR)  --  Portland police say an explosive device that contained a tripwire was found Saturday on a trail near Forest Park.  A bomb squad was dispatched that evening to "Firelane 3" on Northwest Thunder Crest Drive, where the device was found.  Portland Police Sergeant Pete Simpson told KGW-TV that the device was an improvised firearm with a pipe loaded with a shotgun shell.  The matter remains under investigation.