Here is a good site that demolishes creationist claims. http://www.talkorigins.org/indexcc/list.html
For instance, the claim that the Grand Canyon evidences Noah's flood is disposed of this way:
The Grand Canyon was created suddenly by the retreating waters of Noah's Flood.
Austin, Steve, 1995. Grand Canyon: Monument to Catastrophe. Santee, CA: Inst. for Creation Research.
We know what to expect of a sudden massive flood, namely:
a wide, relatively shallow bed, not a deep, sinuous river channel.
anastamosing channels (i.e., a braided river system), not a single, well-developed channel.
coarse-grained sediments, including boulders and gravel, on the floor of the canyon.
streamlined relict islands.
The Scablands in Washington state were produced by such a flood and show such features (Allen et al. 1986; Baker 1978; Bretz 1969; Waitt 1985). Such features are also seen on Mars at Kasei Vallis and Ares Vallis (Baker 1978; NASA Quest n.d.). They do not appear in the Grand Canyon. Compare relief maps of the two areas to see for yourself.
The same flood that was supposed to carve the Grand Canyon was also supposed to lay down the miles of sediment (and a few lava flows) from which the canyon is carved. A single flood cannot do both. Creationists claim that the year of the Flood included several geological events, but that still stretches credulity.
The Grand Canyon contains some major meanders. Upstream of the Grand Canyon, the San Juan River (around Gooseneck State Park, southeast Utah) has some of the most extreme meandering imaginable. The canyon is 1,000 feet high, with the river flowing five miles while progressing one mile as the crow flies (American Southwest n.d.). There is no way a single massive flood could carve this.
Recent flood sediments would be unconsolidated. If the Grand Canyon were carved in unconsolidated sediments, the sides of the canyon would show obvious slumping.
The inner canyon is carved into the strongly metamorphosed sediments of the Vishnu Group, which are separated by an angular unconformity from the overlying sedimentary rocks, and also in the Zoroaster Granite, which intrudes the Vishnu Group. These rocks, by all accounts, would have been quite hard before the Flood began.
Along the Grand Canyon are tributaries, which are as deep as the Grand Canyon itself. These tributaries are roughly perpendicular to the main canyon. A sudden massive flood would not produce such a pattern.
Sediment from the Colorado River has been shifted northward over the years by movement along the San Andreas and related faults (Winker and Kidwell 1986). Such movement of the delta sediment would not occur if the canyon were carved as a single event.
The lakes that Austin proposed as the source for the carving floodwaters are not large compared with the Grand Canyon itself. The flood would have to remove more material than the floodwaters themselves.
If a brief interlude of rushing water produced the Grand Canyon, there should be many more such canyons. Why are there not other grand canyons surrounding all the margins of all continents?
There is a perfectly satisfactory gradual explanation for the formation of the Grand Canyon that avoids all these problems. Sediments deposited about two billion years ago were metamorphosed and intruded by granite to become today's basement layers. Other sediments were deposited in the late Proterozoic and were subsequently folded, faulted, and eroded. More sediments were deposited in the Paleozoic and Mesozoic, with a period of erosion in between. The Colorado Plateau started rising gradually about seventy million years ago. As it rose, existing rivers deepened, carving through the previous sediments (Harris and Kiver 1985, 273-282).
Woolf, Jon, 1999. Young-earth creationism and the geology of the Grand Canyon. http://www.jwoolfden.com/gc_intro.html
Allen, J. A. et al., 1986. (see below)
American Southwest, n.d., Mexican Hat. http://www.americansouthwest.net/utah/mexican_hat/index.html
For photos, see http://www.americansouthwest.net/utah/mexican_hat/goose2_l.html
Baker, V. R., 1978. The Spokane flood controversy and the Martian outflow channels. Science 202: 1249-1256.
Bretz, J. H., 1969. The Lake Missoula floods and the Channeled Scabland. Journal of Geology 77: 505-543.
NASA Quest, n.d. Mars Team online photo gallery. http://quest.arc.nasa.gov/mars/photos/pathfinder.html; see especially http://quest.arc.nasa.gov/mars/photos/images/marspfsite.gif
Harris, D. V. and E. P. Kiver, 1985. The Geologic Story of the National Parks and Monuments. New York: Wiley.
Waitt, R. B. Jr., 1985. Case for periodic, colossal jökulhlaups from Pleistocene glacial Lake Missoula. Geological Society of America Bulletin 96: 1271-1286.
Winker, C. D., and S. M. Kidwell, 1986. Paleocurrent evidence for lateral displacement of the Pliocene Colorado River delta by the San Andreas fault system, southeastern California. Geology 14: 788-791.
Allen, J. A., M. Burns and S. C. Sargent, 1986. Cataclysms on the Columbia. Portland, OR: Timber Press.
Beus, S. S. and M. Morales (eds.), 2002. Grand Canyon Geology, 2nd edition. London: Oxford University Press. (technical)
Chronic, Halka, 1983. Roadside Geology of Arizona. Missoula: Mountain Press Publishing.
Elders, Wilfred A., 1998. Bibliolatry in the Grand Canyon. Reports of the National Center for Science Education 18(4) (July/Aug.): 8-15.