This is Douglas Nightshade (Solanum douglasii). Carol and I saw this along the road, around bridge 6, if memory serves. (And if it doesn't, perhaps I've been smoking too much nightshade.) The other Solanum species in the canyon is Solanum elaeagnifolium or Silverleaf Nightshade.
Photo by Carol Tornow, 9/26/11
This is the other Datura species in the canyon. Desert Thorn Apple (Datura discolor). Look closely into the flower and you'll see the distinctive purple streaks. Those purple streaks are not found in the Sacred Datura (Datura wrightii). This lone plant was found about 1/4 into the canyon along the left side of the road.