An asscrack so deep, so treacherous, that there is a real danger of falling in or losing one's wallet, hat and shoes during any encounter, i.e. anal-sex, getting too close to one on an up-escalator, attempting to extract a wedgie.
"Yo yo yo, I be fallin into that ho's turd-canyon when I poonjabi'd that bitch last night! I still can't find my cell!"
"Momma always told me yo, 'Don't be wif a wimmins who got a turd-canyon you cain't climb out uv!' an I shoulda listened yo!"