As clear and blue as its better-known namesake, just mini. While volcanic collapse created the original, this pocket-size model emerged as a frigid artesian spring dissolved an area of limestone. The log-strewn lakebed, 45 feet below, is visible from the surface. Sorry, no swimming.

Ninety-ton boulder, very large and vaguely trapezoidal, made of a fine-grained sedimentary rock called argillite. Carried by Ice Age megafloods from Northern Rocky Mountains, when Glacial Lake Missoula repeatedly burst through its frozen dam and water surged west. Also deposited: the rich topsoil that makes the Willamette Valley so fertile.

So-called drainpipe of the Pacific. Bowl-shaped, 20-foot-deep hole in the basalt shoreline likely formed by the collapse of a sea cave. Seawater pours in, as if sucked, and splashes back out. Level of drama depends on the tide.

Undulating claystone slopes striped in shades of rust, gold, yellow, and black. Color bands are due in part to cycling changes of climate over millennia, as warm and wet conditions gave way to dry and cool periods. Live up to the hype.

Modest name belies the radness of this two-mile-long volcanic fissure, as deep as 70 feet in spots. Fairly easy hike, with some playful clambering. Pack layers: Temps can be up to 20 degrees cooler at the bottom than at ground level.

Formed over millions of years by slightly acidic water seeping into marble. The result: winding passageways, grand chambers, and stalactites and stalagmites galore. Accessible only via guided tour; a three-hour off-trail excursion requires belly crawling. 

Carved by the Snake, a max depth of about 8,000 feet makes this the deepest river gorge in North America (take that, Grand Canyon). Mostly inaccessible by road. Extraordinary whitewater rafting, backpacking, and horseback riding.

Stately, fossil-bearing rock formations reminiscent of ancient Roman ruins. Columns of weathered rock stand up to 100 feet tall and span five miles in one direction and two miles in the other. On private property but viewable via well-maintained gravel road.