The journey starts at Castolon, which sits on a hill at 2,169 feet msl overlooking the river. Cottonwood Campground, and its parking area, are located at the put-in. Eight NPS primitive campsites are conveniently located along the river below the put-in. The trip could be a hard 2-day paddle, though most boaters will take at least 3-4 days to leisurely navigate the river, taking time to enjoy the natural beauty of the desert and perhaps explore some of the adjacent areas. Crossing into Mexico is very easy, and also very illegal, with stiff fines for those caught re-entering the US other than at the border crossings in Del Rio or Presidio, each a LONG way from this reach of the river, so cross at your own risk! The Chisos Mountains are on river left, though they are some distance away. Several small, and usually dry, creeks enter the river from the Texas side along the way. There are no distinctive landmarks, roads, inhabited towns or much of anything else on this reach, so be sure to pack everything you will need, but travel as lightly as possible. The river can flash during the late-fall monsoon season, which is usually about the only time you can paddle here, so be sure to pay attention to weather and climate conditions, and camp well above the river's edge to avoid a surprise in the middle of the night.

In addition to other critters, Big Bend National Park is home to one species of copperheads and four species of rattlesnakes, but you will not see them during daylight most of the time because they are hiding from the scoarching sun and temperatures that can reach nearly 120° F from June into September, though the normal season will have milder conditions, often being cool to wam during the day and downright cold at night. Those long, and very fast, reddish snakes are non-poisonous coachwhips, sometimes called Red Racers, and you are not likely to get near one of them! The have a fear of humans that prompts a fast departure when you approach. However, tarantulas and scorpions, may not flee at all, the latter being the most likely source of any real problems you encounter. I never saw any rattlesnakes or copperheads during the times I spent in Big Bend, but I know they are there, so these warnings are given as a precaution. If going during the October through March normal season, then you are not very likely to see them at all!

Take a camera, because this is a river like you have never paddled before, and you will want to preserve memories of it for a long time to come. Going the 47 miles from Castolon to Talley will let you know why it is called "The Great Unknown". This is not a trip for casual paddlers, and will be one most enjoyed by those who prefer true wilderness adventures. Be prepared for hot, cold, wet and dry conditions.

Far southwest Texas, in Brewster County in the Big Bend area of the Rio Grande Valley along the Texas-Mexico border between Santa Elena and Mariscal Canyons.

Dallas 520 miles; El Paso 340 miles; San Antonio 425 miles; Houston 625 miles; Austin 440 miles (all distances are approximate and depend upon starting point, destination point on the river and route taken.)

Water quality is usually good to very good at navigable levels, though it will be brown and muddy, with a lot of grit. The sand along the banks will be very dry and powdery except after flooding, when it becomes thick mud (Rio Grande mud!) Flows were abnormally low for several years, but have increased significantly since 2003. The river can and will rise quickly after rain upriver in the Presidio area. Flows are generally adequate for canoeing, though rafting may be limited in months of low flows.

Early November through mid-March is generally the best time to paddle the Rio Grande. Summertime temperatures can soar above 100° F. Spring and Fall are frought with the possibilities of flash floods. BBNP off-river camping areas are limited and may be very crowded during holiday periods or during the winter "snowbird" season, which is also the time most likely to have favorable paddling conditions. Summertime low-water conditions may be inadequate for rafting, but canoes can almost always navigate the river.

Entrance permits to Big Bend National Park are required for all vehicles entering the park for river access. Fees are $20.00 per vehicle (increasing to $25.00 in 2015) and allow park access for up to seven consecutive days. Leaving vehicles overnight in a campsite also requires an additional fee of $10.00 per car per night (there is no additional fee for leaving cars in designated parking lots, but you do need to get an "overnight pass" for your dashboard so that rangers will know yours is not an abandoned vehicle.) Backcountry permits ($10.00 per group / $5.00 with Senior Pass), issued by Big Bend National Park and available through local outfitters and BBNP Ranger Stations, are required for all trips on or along the Rio Grande by automobile or boat at all times. River runners in The Great Unknown are limited to a maximum group size of 30 people, and groups must launch at least two hours apart. Groups are not allowed to stop, eat or camp together along the river. For more information, call Big Bend National Park at (432) 477-2251.

There are no significant hazards to navigation along this reach of the river, though it would be a major hazard if you were to get caught without adequate water for paddling, and even worse if you ran out of water to drink! This is primarily a flatwater run with only occasional small rapids or fast currents. Off-river hazards COULD include desert heat, snakes, scorpions, bears, mountain lions or other potential threats to safety.

Put in at Castolon at 0.0 miles. Take out at Talley at about 47.0 miles. There are no other practical access points for this section of the Rio Grande. In an emergency, and with aid of a high-clearance, 4-wheel drive vehicle, egress could be made along River Road West at any of the primitive campsites unless it has been raining around the river, in which case the road will be impassable. Auto theft and vandalism is a recurring problem at backcountry parking areas, so do not leave unattended vehicles there if not necessary, and do not leave valuables inside vehicles. If valuables must be left with a vehicle, then make sure they are locked securely in the trunk.

The National Park Service provides nine primitive, backcountry campsites, including the ones at the access points, along this reach of the river. Backcountry permits are required for paddling and building fires, and are available from park rangers without charge. However, each vehicle must remit $20 per week (increasing to $25.00 in 2015) for access to the park, plus $10 per night for each night it remains in the park. It is unlikely that you will have to fight for campsites on this reach of the river. Most BBNP visitors stay in the Chisos Basin or Rio Grande Village campgrounds. RGV has the only showers and laundry facilities in BBNP, as well as a store, 100 tent sites, 25 RV sites with full hook-ups, flush toilets and a dump station. Chisos Basin has 65 tent sites, flush toilets, a dump station and the only restaurant in BBNP (food is okay and lunch rates are reasonable, though dinner rates are much higher, but where else are you gonna go? The nearest outside food is about 25 miles away in Study Butte or Terlingua!) Cottonwood has 35 tent sites and pit toilets (generators are NOT allowed!) All campgrounds have lockers to keep javelinas and other animals from getting to your food, soap, deodorant, toothpaste and other things with a fragrance. Chison Basin has bear-proof lockers, though I never saw any signs of ANY animals there.

There are at least four known commercial outfitters offering rentals, shuttles, guided trips and/or river information for this reach of the Rio Grande.

Most people who paddle the Rio Grande come for the beautiful canyons. This reach is a desert adventure between canyons, where you can look out across miles of sand, cactus, yucca, century plant, ocotillo, sotol, lechuguilla and other desert vegetation. The trip is long, and at 47 miles it discourages recreational paddlers who are not into desert wilderness camping trips. The craft of choice is a canoe because it can carry everything you need, so if you are a kayaker, then be especially nice to your friends who paddle open boats. Rafts can make this trip, but they will be slow, and if the water is low, then the task of getting downriver will be even harder. Be sure to obtain your backcountry permit from park rangers before setting out, and allow plenty of time for setting up your shuttles, because the drive is much longer than the downriver distance. The fast route between Castolon and Solis is about 70 miles or more, with about 14.5 miles across very unimproved roads where top speed will usually be 5-10 mph. There are shorter routes, if you have a high-clearance, 4-wheel drive vehicle, but the time to drive it would be much longer. The direct route is not MY idea of a river road! In fact, it is hardly a road at all, but rather a graded path across the desert floor with lots of places to get stuck. A shuttle bunny would be just what the doctor ordered! Bring your camera, plenty of drinking water and everything you need for boating, camping, eating and personal hygiene. Be sure to pack out everything you pack in, and take nothing from the desert except memories. Removing plants, animals, artifacts or other things you find there is a crime! This is a very special place for those who enjoy going where few others will ever paddle.