This is an ancient (silted over, filled in) canal leading from the center of Matamoros , Mexico out to the Gulf. The original ocean breakwaters are worn away and nearly disintegrated, and the canal proper inland has been nearly obliterated by sand and debris wash that looks like tsunami debris. In any case, the sand and tide and tidal incursion as tsunami debris has covered the first 11 miles of this system. The first five miles from the current ocean shore has been almost completely obliterated by high dune like structures of what appears to be tsunami debris.
Photo courtesy of NASA.
There are outlines of rectangular forms on the ground facing the banks of the canal 3 miles inland that suggests some form of buildings or structured land use prior to the devastation. All remnants of that use seem to have disappeared with the extreme nature of the destruction. About 12 miles inland is where the heavy wash and residue seems to diminish. There is no apparent effect further inland. A twelve mile incursion with a heavy shore side debris field depth measured in meters suggests a very strong and very high tsunami. In my estimation, the tidal height may have been measured in the low hundreds of feet.
Photo courtesy of NASA