East of Mosier, a section of the Historic Columbia River Highway  begins again for automobile traffic, climbing up over a spectacular volcanic promontory called Rowena Crest. For eastbound traffic, this route begins at Mosier, at I-84 Exit 69, while westbound traffic can pick up the route at I-84 Exit 76.
Almost nowhere else can you see both the dry eastern and wetter western faces of the Columbia River Gorge  with such clarity and distinction as at Rowena Crest. The dark Columbia River basalt cliffs are derived from massive lava flows 15 million years ago. The terracing of the region was due to the action of the Missoula Floods on the Columbia Plateau fault scarps.
More information on the geology and ecosystem is available from a free pamphlet in the drop box on the north side of the highway, courtesy of the Tom McCall Nature Preserve. This 2,300-acre sanctuary on part of Rowena Crest was created by the Nature Conservancy and has trails on the hillsides that are open to the public.
These cliffs represented the beginning of the last hurdle facing Willamette Valley –bound Oregon Trail pioneers. After Rowena, the Gorge cliffs rose so high that the pioneers were forced either to build rafts and float the then-hazardous rapids on the river, or to follow the Barlow Trail around the south flank of Mount Hood .
Today, Tom McCall Nature Preserve is the site of a mid-May pilgrimage by wildflower lovers. Because the preserve lies in the transition zone between the wet west and the dry east, several hundred species flourish here, including four that occur nowhere else in the world. Included in the spring display are yellow wild sunflowers, purple blooms of shooting stars, scarlet Indian paintbrush, and blue-flowered camas.
While the flowers are enticing, be careful of ticks and poison oak. Of course, as with any nature preserve or public park, love the flowers but leave them behind for the next person to enjoy.