Pontmorlais is the area around the top of High Street in the centre of Merthyr. It is near where the world's first steam locomotive, developed in 1804 by Cornishman Richard Trevithick, ran down what is still called the Old Tramroad.
It was also a street name and (as Pontmorlais West) still exists.
Pontmorlais means "the bridge over the Morlais (Brook)".
Regards (and welcome to Rootschat),
Gareth
PS. Just a thought: if you include the name of the place (in this case Merthyr, Pontmorlais or both) in the title of your post, it's more likely to catch the eye of someone familiar with the area.