Some people call these things descending indexes, but they are really regular indexes with a column in descending order. Once you specify "DESC" in a column expression, you are telling Oracle to make it descending.
Indexes with descending columns are really function-based indexes. COLUMN_NAME in DBA_IND_COLUMNS will show something like SYS_NC00002$. To find the real column expression, you have to go looking in DBA_IND_EXPRESSIONS.
(And there's a silly side-effect of this. But more on that in a moment.)