Great pic's and report.
It was a good decision to turn around while trying to travel the east side of Mono Lake. I was just there in my Jeep in May and took the same road. After about 6-7 miles, if I recall correctly, the road runs into pure sand dunes. We were by ourselves, so turned around also.
Cheap video from inside the Jeep of the road you were on.
There is a road further east of Mono that would work just fine. I drove it in the Jeep in 2W and it has "light" sand. In otherwords not deep sand and simmiliar to Cottonwood road. I'd recommend it.