Cov qhov rooj hluav taws kub hlau, zoo li lub qhov rooj hluav taws ntoo, muaj cov qib tiv thaiv hluav taws sib raug zoo, uas tau muab faib ua peb qib: A, B, thiab C. Qhov kev txwv qhov hluav taws kub ntawm Chav B qhov rooj hluav taws yog 60 feeb. Thaum lub qhov rooj tua hluav taws raug teeb tsa, cov hluav taws kub hnyiab yuav muab ntxiv rau txhua qhov sib txawv, uas tuaj yeem thaiv cov pa phem los ntawm kev khiav tawm sab nraud ntawm lub qhov rooj.