In Martins book, this is hike 32 on page 74.
In Tomasis book, this is on page 163
Don't confuse Bathtub tank in Adobe Canyon with Bathtub Water in Big Casa Blanca Canyon. They are about 1.5 miles apart and in different canyons.
You drive down highway 83, through Sonoita, then southwest on 82. About 5 miles from Sonoita, between MP 27 and 28 you turn north (right). This will take you up Adobe Canyon. A sign may well designate this as "Adobe Canyon Road". After about 1 mile you reach the Forest boundary and this becomes FSR-234. Before getting here, you may be intimidates by a Private Property sign, but you are within your rights to drive the road to the Forest boundary.
You may be able to drive as much as 4.3 miles from the highway with a good 4x4 vehicle, but this entirely depends on road conditions. Tomasi simply says that FSR-234 is in "miserable condition" and gives no estimate as to how far you may be able to drive. He says you should expect plenty of contact between your vehicle and brush and branches. The alternative is walking, and may well be a good idea anyway as you may be able to walk as fast as you can drive.
If you make it the full 4.3 miles you will almost be at Bathtub Tank. Tomasi gives the mileage as 0.5 miles, but this may be the mileage if you continue on to El Pilar.
Tomasi suggests a loop hike going clockwise and starting up the left arm of upper Adobe Canyon. This will go to Bathtub tank, then over and beyond it. Another concrete dam is at El Pilar. El Pilar is a 50 foot high rock pilar. Doing this as a loop involves crossing east to the other arm of upper Adobe Canyon.
Note that it is also possible to reach this area from above, starting at the Tunnel Spring trailhead and hiking down what Tomasi calls "Gravesite Ridge".
If you see any "black mountain lions" you may have sighted a panther (jaguar?). There have been such sightings in this area. Try to get a photo if you should be so lucky. Look for a long tail if you think you are seeing a mountain lion.
Tom's hiking pages / [email protected]