CREATE TABLE table_name_77 (elevation__ft_ INTEGER, isolation VARCHAR, range VARCHAR, peak_name VARCHAR)
WHAT IS THE ELEVATION OF THE UNAKA MOUNTAINS, IN ROAN HIGH BLUFF PEAK, AND ISOLATION LARGER THAN 1.54?
SELECT AVG(elevation__ft_) FROM table_name_77 WHERE range = "unaka mountains" AND peak_name = "roan high bluff" AND isolation > 1.54