Elk Rock Island is a not-always-accessible by land spot on the Willamette River in Milwaukie, connected to the mainland by a land bridge at low water. It is accessible from the Spring Park trailhead on SE 19th Avenue and Sparrow Street. From Portland Parks and Recreation:
The island represents part of an ancient volcano that erupted about 40 million years ago. The large, jagged rocks (Waverly Heights basalt) found throughout the island were formed by lava flows, and may be the oldest exposed rock in the Portland area. The island contains seven distinct habitats, including wetlands, forests and grasslands. A number of birds, including bald eagles and osprey, have been spotted in the area.
Patrick and I spent about two hours exploring there on August 19th (photos):
A Green Heron:
Love the moon in the background of this shot:
Botanists at work: