Summer Lake, 10 miles north of Paisley, is blue-green and slightly kidney-shaped, surrounded by miles of crusty evaporation pans. It was once much larger. When the glaciers melted in the Cascades 10,000 years ago at the end of the Ice Age, they pumped big rivers into this country, making it more like lake-country Minnesota than high-desert Oregon. Summer Lake has been shrinking ever since.

The caves, in a lone basalt outcrop, gaze across prehistoric Summer Lake, now an ocean of sage. All you can see of the lake is a silvery sheen in the distance. The sun was setting through rain that would slowly turn into light snow. I carried my pack around the north sweep of the outcrop and camped there, one of the caves looking down on me as long rollers of clouds spilled over the Cascade foothills.

As the sun broke through underneath the cloud-ceiling, a double rainbow balanced on the rocky point, curving toward the caves as if to make sure I noticed them.

Rule #3 for time-travelers: Notice everything, because everything is a sign.

I didn't go into the caves right away. Instead, I climbed a few hundred feet to the top of the point, where the two rainbows had landed, and surveyed a horizon of sage, trying to imagine what it used to be like.

Rule #4: Visit existing places similar to those you are trying to imagine.

The easiest place to get a sense of what the former shoreline was like is the Summer Lake State Wildlife Area, where the Ana River enters the lake from the north. It is a landscape of abundance, filled with mud-runners and mewing rails, ivory-statue egrets and the ungainly calls of gulls. Northern harriers skim the marshes. Terns plow into the water, come up with fish and then launch into the sky.

I transposed that wildlife area onto the front porch of my caves, picturing a sort of Ice Age paradise once rich with birds and fish. The easy pickings must have been a relief for Pleistocene nomads accustomed to tackling unfriendly megafauna, with wooden shafts and sharpened stones.

As I watched sunset rays plunge through rainsqualls, a coyote called with high whoops and whines.

Replace the coyote's yelp with the throaty howl of an extinct dire wolf, and the hair will perk on the back of your neck.

The next morning, I explored the caves. Facing into prevailing winds, they were well-suited for summer camps. I stood at the entrance of each one, looking out on sage that was once water. The original shoreline of Summer Lake would have been about a mile from here, instead of five miles. People would have camped in these shelters, but most of their time would have been spent out there, on the abundant shore.

Rule #5: Go wherever your eye lingers.

I left the caves and walked into miles of ancient shorelines, reading pebbles on the pages of long-vanished wave-washed beaches. Crackled hardpan became former marshland. I found broken arrowheads and obsidian scrapers, signs the shore was once in heavy use. I picked up each piece, studying its finely flaked edges before putting it back. This technology was, at most, 1,500 years old, not that of the oldest people. Still, 1,500 years is a very long time, and the artifacts told their own stories.

Rule #6: There is never just one time.

I found a broken obsidian arrowhead so translucent that when I held it to the sun, it looked like a sliver of ice. Peering through it, I looked back through thousands of years. A hunter moved along the edge of a slowly receding marsh. I heard the sounds of the birds and fishtails slapping against the reeds in that shallow water. Perhaps the arrowhead fell out of the hunter's pouch, or was carried off in the flesh of an animal that escaped.

I lowered my obsidian telescope and the ancient lake disappeared, replaced with Oregon sage, a fleeting landscape in itself. This is how you time travel, learning to see the era you live in differently, realizing you already live in the past.