The beach is amazing. It is really out in the middle of no where. It is a striking bay that is lined by white sand. You will very rarely see anyone out in this area.
The water temperature here can vary greatly with the swell direction. One day you can be in board shorts and the next day you may need a wetsuit. Best is to bring it all and dip your toe in the water.
To get to Tres Cruces you will need to get a guide. It is out in the middle of no where and there is a fair amount of driving on winding dirt roads. You can contact guides in Mancora.
Be respectful of the locals and if there are people surfing always give them the right away. Also, the place is pristine and beautiful. Keep it that way by bring out all of your trash. As a matter of fact, if you see some trash there pick it up and take it with you.