Clark Ashton Smith sounds like a firm of estate agents, was in fact a pulp weird fiction writer, contemporary and bestie pen pal of H P Lovecraft, writing in the 20's and 30's.
I acquired a second-hand short story collection, Genius Loci,because of the HPL connection, and jumped right in. It's a mix of horror, fantasy and SF which reminds you forcefully just how weak the boundaries were between genres during the first blossoming of mass market speculative fiction.
Genius Loci demonstrates CAS's chief accomplishment as a writer: depicting the gruesome, haunting image. Whether it's Hobbes' leviathan made flesh through dark sorcery (The Colossus of Ylourgne) a garden adorned with grafted body parts (The Garden of Adompha), or a statue of the goddess of love entwined with an amorous corpse (The Disinterment of Venus) the images remain with me even though the stories themselves may sometimes be ephermeral.
To put it another way, unlike Lovecraft, all horror for CAS is fundamentally describable and speakable.
Smith was an artist as well as an author, and while a flippant response to his work would be to say as a writer he makes a pretty good painter, it's interesting to see the uncanniness of his pulp fiction as a pop counterpart to the visual revolution of surrealism happening at the same time across the Atlantic in a very different milieu. This may well be a strong misreading of his influences, but I prefer to see it as the same cultural currents coming to the surface in different ways.
Certainly, reading CAS reminds me of nothing more than Dali's photorealist nightmares.
But does Clark Ashton Smith still matter, three-quarters of a century later? Well, the SF tales are hard going, tending towards the dated OMG it's a polygon from Pluto strain also found in Lovecraft, the prose regularly empurples, and his attitudes to women (victims, fiancees and concubines, in the main) are very much of his time. Yet in spite of all this, he cuts through all this back to the original Gothic spirit of awful sublimity in a way which would do Ann Radcliffe proud.
And it's telling that a pulp writer working in your grandparents' or great-grandparents' idiom has bags more imagination and creativity, more downright erudition placed in the service of his craft, than most fantasy authors today. If we can't match the high-water marks of interwar weird fiction, then frankly the genre is in trouble.
Postscript: while drafting this review I came across a rather splendid academic/fan site for Smith - The Eldritch Dark. Here you can read some of his works, view his work, consider literary criticism and even hear some of his stories read out loud.