The following is a first hand account of the danger of flash floods in the San Rafael Swell. As told by an unknown person who visited the Swell.
On August 8, 1992, my husband and I began our loop hike with Little Wild Horse Canyon. We we delighted by the dazzling beauty around every swirling curve of the canyon as we made our leisurely way toward Bell Canyon. Out on the dirt road, we caught our first glimpse of the full sky since we started our hike; there was a killer storm brewing. We just entered the mouth of Bell Canyon as the rain started. We took shelter under a rock as the rain quickly became a downpour and just as suddenly turned to hail. Within minutes we could not see the other side of the canyon, the hail was so intense. The hail/rain continued for about 30 minutes and during that time, the flood began. That nice, dry canyon (it clearly had not had significant rain for a long time) soon changed dramatically. Ever marvel at how tree trunks get lodged between canyon walls 30 feet above your head? We found out on this day. The water came down the gulch gradually, a wave at a time; the first wave was only a few inches deep, then 5 minutes later another wave, bigger than the first, and so on until the water coming from our storm, from the top of the mesa, from all the canyons draining into Bell Canyon and from the mountains combined to create a raging river that filled the canyon to ten feet deep. Whole trees floated by us while the walls of the canyon beneath our feet rumbled and shook as boulders were washed down with the current. The unmistakable smell of pine trees floated down in drafts of cold mountain air as we stared with wonder at the spectacle before us. We could not leave the place we were in. We watched as the water kept climbing higher, eliminating "islands" and washing over high ground we thought was safe. Sand waves formed and disappeared before our eves. We remained trapped for 2-3 hours before the water level went down to where we thought we could navigate it.
The water was 45 degrees (at the most), and painful to walk in. All of those lovely narrows in Bell Canyon became swimming holes. It was a cold, miserable journey out of the canyon.
When we finally got out, our troubles were just beginning. Four 4X4 vehicles had parked in the wash at the opening to the canyons. Ours was the only one still standing. A jeep had been washed 1/2 mile down the canyon, an Isuzu Trooper was about 1/4 mile down, laying on its side with an imploded windshield. A Toyota had been pushed by the water into a large boulder where it became lodged as water rushed up the bed, broke the glass in the cab and filled it with water, mud and debris.
Our car fared the best; nothing was broken. The water had gotten inside (about one foot deep), and the entire engine was filled with silt. Luckily, all of our camping gear was dry in the back of the vehicle and we retreated to high ground to spend the night. The water stopped running completely around midnight.
Don't let this happen to you! There is high-ground parking about 1/4 mile south of the entrance to the canyons. While you are in the canyon you have no way of knowing if there is a storm brewing, and it doesn't have to rain where you are to flood. Little Wild Horse Canyon is very narrow and our chances of survival in this flood would have been very slim. Be aware and prepared for bad weather at all time. Late summer/early fall afternoon thunderstorms are common in Southern Utah.