The traditional idea that all were originally quarried at Chunar, just south of Varanasi and taken to their sites, before or after carving, "can no longer be confidently asserted", and instead it seems that the columns were carved in two types of stone.
Some were of the spotted red and white sandstone from the region of Mathura, the others of buff-colored fine grained hard sandstone usually with small black spots quarried in the Chunar near Varanasi.
The uniformity of style in the pillar capitals suggests that they were all sculpted by craftsmen from the same region.
It would therefore seem that stone was transported from Mathura and Chunar to the various sites where the pillars have been found, and there was cut and carved by craftsmen.

The pillars have four component parts in two pieces: the three sections of the capitals are made in a single piece, often of a different stone to that of the monolithic shaft to which they are attached by a large metal dowel.
The shafts are always plain and smooth, circular in cross-section, slightly tapering upwards and always chiselled out of a single piece of stone.
There is no distinct base at the bottom of the shaft.
 The lower parts of the capitals have the shape and appearance of a gently arched bell formed of lotus petals.
The abaci are of two types: square and plain and circular and decorated and these are of different proportions.
The crowning animals are masterpieces of Mauryan art, shown either seated or standing, always in the round and chiselled as a single piece with the abaci.
 Presumably all or most of the other columns that now lack them once had capitals and animals.
They are also used to commemorate the events of the Buddha's life.

Currently seven animal sculptures from Ashoka pillars survive.
These form "the first important group of Indian stone sculpture", though it is thought they derive from an existing tradition of wooden columns topped by animal sculptures in copper, none of which have survived.
It is also possible that some of the stone pillars predate Ashoka's reign.
The traditional idea that all were originally quarried at Chunar, just south of Varanasi and taken to their sites, before or after carving, "can no longer be confidently asserted", and instead it seems that the columns were carved in two types of stone. Some were of the spotted red and white sandstone from the region of Mathura, the others of buff-colored fine grained hard sandstone usually with small black spots quarried in the Chunar near Varanasi. The uniformity of style in the pillar capitals suggests that they were all sculpted by craftsmen from the same region. It would therefore seem that stone was transported from Mathura and Chunar to the various sites where the pillars have been found, and there was cut and carved by craftsmen.
The pillars have four component parts in two pieces: the three sections of the capitals are made in a single piece, often of a different stone to that of the monolithic shaft to which they are attached by a large metal dowel. The shafts are always plain and smooth, circular in cross-section, slightly tapering upwards and always chiselled out of a single piece of stone. There is no distinct base at the bottom of the shaft.  The lower parts of the capitals have the shape and appearance of a gently arched bell formed of lotus petals. The abaci are of two types: square and plain and circular and decorated and these are of different proportions. The crowning animals are masterpieces of Mauryan art, shown either seated or standing, always in the round and chiselled as a single piece with the abaci.  Presumably all or most of the other columns that now lack them once had capitals and animals. They are also used to commemorate the events of the Buddha's life.
Currently seven animal sculptures from Ashoka pillars survive. These form "the first important group of Indian stone sculpture", though it is thought they derive from an existing tradition of wooden columns topped by animal sculptures in copper, none of which have survived. It is also possible that some of the stone pillars predate Ashoka's reign.
Pillars of Ashoka