Big Bend Ranch State Park. The park's website says this:
"The Rio Grande/Rio Bravo corridor is an easily accessible area of the park for day use, including rafting, canoeing and free bank fishing. Several river access points are found within the park along FM-170. Colorado Canyon includes Class II and Class III rapids. This section of the river is not considered dangerous under normal flow conditions. The walls of Colorado Canyon, unlike the limestone canyons of Big Bend National Park and the Lower Canyons, are entirely of igneous rock."
We'll report on our own canoe trip with an outfitter in the coming days...stay tuned!