There are several types of barrel cactus but I only saw this variety at Alabama Hills.
The brown spots are withered up flowers from spring.
As big as barrel cactus can be, their flowers are very small.
The spines besides being very sharp are also extremely hard.
You could use one as a sewing needle for canvas, that's how tough they are.
This is another variety which I have one of at home in addition to the above.