Finding date intersections

I have a table of sales that have possibly overlapping time ranges. I want
to find all the timeranges where there's an active sale. How would you do
that?

create table sales (
times tstzrange
);

insert into sales values
(tstzrange('2014-1-1', '2014-1-2')),
(tstzrange('2014-1-2', '2014-1-3')),
(tstzrange('2014-1-2', '2014-1-4')),
(tstzrange('2014-1-5', '2014-1-6'));

-- want back:
-- tstzrange('2014-1-1', '2014-1-4')
-- tstzrange('2014-1-6', '2014-1-6')

Thanks,
Joe