The Hartford Courant has a story on new dating of the Grand Canyon, long thought by creationists to reflect a recent creation. The article outlines the question thus:
Within the United States, the most common psychological yardstick for Earth's antiquity is the Grand Canyon in Arizona. Seeing it from above is unforgettable. One is immediately struck by the mile-deep chasm beneath the Colorado Plateau. Seeing it from below is also unforgettable. The erosive power of its foaming, grit-laced rapids is self-evident. Could such a canyon be carved in only 5,000 years, as young Earth creationists suggest? Was it cut by single torrent when Noah's flood drained away?
It then answers its own question:
It turns out that the Grand Canyon is really two canyons, an older one to the west and a younger one to the east. The western canyon began to form about 20 million years ago by the progressive erosion of a small river system toward its head. This erosion took place at an average rate of about one-quarter of one-thousandth of a foot per year. In the eastern canyon, the rate of erosion is double that rate, and didn't begin in earnest until about 4 million years ago. This was shortly after the eastern and western watersheds merged to become a through-going river.
Three points emerge from this study that should be heeded by those tempted to accept young Earth creationism as a matter of faith. First, the story of an older and younger canyon merging is inconsistent with the notion of a single biblical deluge. Second, canyon cutting is a fairly steady process, not a catastrophic one. Third, the long-term rate of erosion demands that the process began 4,000 times earlier than the young Earth creationists would suggest.
Read the article to see how they did it. Not a shining day for the YECs. This pretty much confirms that which we always thought: the Grand Canyon reflects the accurate age of the earth. Here is TalkOrigins' critique of the ICR's Grand Canyon Dating papers.