Lovecraft actively encouraged his correspondents and peers to not only use his body of work as inspiration but to also add to his creations both organic and inorganic. The body of Lovecrafts work contained themes that became known as the Cthulhu Mythos, which since his death has taken on a life of his own. During his life and for some time after Smith took up Lovecrafts offer and both used his works and added his own elements to the Cthulhu Mythos. Below is a list of Smith's stories and poems that have been classified as 'Cthulhu Mythos' works by Chris Jarocha-Ernst. I have added footnotes and links but the list is copyrighted by Chris Jarocha-Ernst 1996. For more info see: Klarkash-Ton and the Cthulhu Mythos By Chris Jarocha-Ernst.

Boyd's note: I Personally prefer Lin Carters and Clark Ashton Smith's list of CAS works that belong in the Cthulhu Mythos, but Jarocha-Ernst is the longer so ill use it. Smiths selections are denoted by the (1) footnote; Carters by (2).

• The Muse of Atlantis, in Ebony and Crystal: Poems in Verse and Prose, Auburn, CA: 1922. mentions Atlantis.
• The End of the Story, Weird Tales, Vol. 15, No. 5, May 1930. Mentions Averoigne, France; Perigon; Vyones, France; Chateau des Faussesflammes; Lamias.
• The Last Incantation, Weird Tales, Vol. 15, No. 6, June 1930. Mentions Poseidonis; Malygris; Hyperborea; Susran.
• The Uncharted Isle, Weird Tales, Vol. 16, No. 5, November 1930. Mentions Lemuria; Mu.
• A Rendezvous in Averoigne, Weird Tales, Vol. 17, No. 3, April-May 1931. Mentions Averoigne, France; Vyones, France; La Frênaie, France; Chateau des Faussesflammes; Vampires.
• The Satyr, La Paree Stories, July 1931. Mentions Averoigne, France; La Frênaie, France; Satyrs.
• The City of the Singing Flame, Wonder Stories, July 1931. Mentions Hastane, Philip; Singing Flame; Angarth, Giles; Ebbonly, Felix; Ydmos.
• A Voyage to Sfanomoë, Weird Tales, Vol. 18, No. 1, August 1931. Mentions Poseidonis; Sfanomoë (Venus); Antillia; Moaria; Moon; Atlantis; Lephara.
• The Return of the Sorcerer ^{1 2}, Strange Tales, September 1931. Mentions Necronomicon; Carnby, John; Al Azif; Ghouls.
• The Tale of Satampra Zeiros ^{1 2}, Weird Tales, Vol. 18, No. 4, November 1931. Mentions Tsathoggua; Satampra Zeiros; Tirouv Ompallion; Uzuldaroum; Hyperborea; Commoriom; Lemuria; Polarion; White Sybil; Black Slime.
• Beyond the Singing Flame, Wonder Stories, November 1931. Mentions Hastane, Philip; Singing Flame; Angarth, Giles; Ebbonly, Felix; (Ydmos).
• The Door into Saturn ^{1 2}, Strange Stories, January 1932. Mentions Cykranosh (Saturn); Eibon; Zhothaqquah (Tsathoggua); Yhoundeh; Mhu Thulan; Hziulquoigmnzhah; Hyperborea; Bhlemphroims; Vhlorrh; Ydheems; Djhenquomh; Djhibbis; Ghlonghs; Ghlomph.
• The Vaults of Yoh-Vombis, Weird Tales, Vol. 19, No. 5, May 1932. Mentions Aihais; Mars; Yoh-Vombis; Ignarh; Venus; Yorhis; Leeches of Yoh-Vombis; Necromantic Ones.
• The Nameless Offspring ^{1 2}, Strange Tales, June 1932. Mentions Ghouls; Necronomicon; Alhazred, Abdul.
• The Weird of Avoosl Wuthoqquan ¹, Weird Tales, Vol. 19, No. 6, June 1932. Mentions Tsathoggua; Commoriom; Hyperborea; Mhu Thulan; Tscho Vulpanomi.
• The Maker of Gargoyles, Weird Tales, Vol. 20, No. 2, August 1932. Mentions Averoigne, France; Vyones, France; Cordeliers; La Frênaie, France.
• The Empire of the Necromancers, Weird Tales, Vol. 20, No. 3, September 1932. Mentions Zothique; Cincor; Naat; Tinarath.
• The Hunters from Beyond, Strange Tales, October 1932. Mentions Hastane, Philip; Sincaul, Cyprian; Hunters from Beyond.
• The Testament of Athammaus ¹, Weird Tales, Vol. 20, No. 4, October 1932. Mentions Tsathoggua; Voormis; Commoriom; Uzuldaroum; Hyperborea; Atlantis; Mu; Mhu Thulan; Tscho Vulpanomi; Knygathin Zhaum; Eiglophian Mountains.
• The Ice-Demon, Weird Tales, Vol. 21, No. 4, April 1933. Mentions Hyperborea; Tsathoggua; Iqqua; Mhu Thulan; Polarion; Oggon-Zhai; Ommum-Vog; Uzuldaroum.
• The Devotee of Evil, in The Double Shadow and Other Fantasies, Auburn, CA: Clark Ashton Smith, 1933. Mentions Hastane, Philip; Averaud, Jean.
• The Maze of Maal Dweb (as The Maze of the Enchanter), in The Double Shadow and Other Fantasies, Auburn, CA: 1933. Mentions Athlé; Maal Dweb; Xiccarph.
• The Double Shadow, in The Double Shadow and Other Fantasies, Auburn, CA: Clark Ashton Smith, 1933. Mentions Poseidonis; Malygris; Susran; Atlantis; Thule; Mu; Mayapan; Serpent- People; Hyperborea; Lemuria.
• The Voyage of King Euvoran, in The Double Shadow and Other Fantasies, Auburn, CA: 1933. Mentions Zothique; Ustaim; Sotar; Geol; Xylac; Tosk; Yumatot; Ornava; Ullotroi.
• The Mandrakes, Weird Tales, Vol. 21, No. 2, February 1933. Mentions Averoigne, France; Grenier, Gilles; Isoile.
• The Isle of the Torturers, Weird Tales, Vol. 21, No. 3, March 1933. Mentions Zothique; Yoros; Silver Death; Achernar; Cyntrom; Tasuun; Indaskian Sea; Uccastrog.
• The Dweller in the Gulf (as Dweller in Martian Depths), Wonder Stories, March 1933. Mentions Aihais; Yorhis; Dweller; Mars.
• The Beast of Averoigne, Weird Tales, Vol. 21, No. 5, May 1933. Mentions Averoigne, France; Ximes, France; Sainte Zenobia; Perigon; Chateau des Faussesflammes; Isoile; La Frênaie, France; Vyones, France; Beast of Averoigne; Atlantis; Hyperborea; Eibon.
• Ubbo-Sathla ^{1 2}, Weird Tales, Vol. 22, No. 1, July 1933. Mentions Eibon; Ubbo- Sathla; Zhothaqqua (Tsathoggua); Yok-Zothoth (Yog-Sothoth); Kthulhut (Cthulhu); Hyperborea; Book of Eibon; Necronomicon; Zon Mezzamalech; Mhu Thulan; Elder Tablets; Elder Gods; Serpent-People; Crystal of Zon Mezzamalech.
• A Vintage from Atlantis, Weird Tales, Vol. 22, No. 3, September 1933. Mentions Atlantis; Dwale, Capt. Red Barnaby.
• The Holiness of Azéderac ^{1 2}, Weird Tales, Vol. 22, No. 5, November 1933. Mentions Averoigne, France; Tsathoggua; Yog-Sothoth; Azéderac; Dagon; Ximes, France; (Great) Old Ones; Vyones, France; Book of Eibon; Eibon; Hyperborea; La Frênaie, France; Druids.
• The White Sybil, in Science Fantasy Booklet Number One, William Crawford, ed., Everett, PA: Fantasy Publications, 1934. Mentions Hyperborea; Mhu Thulan; Cerngoth; Commoriom; Tscho Vulpanomi; Mu; Antillia; Polarion; White Sybil.
• The Ghoul, The Fantasy Fan, January 1934. Mentions Ghouls; Vathek. Lin Carter considered this to be part of the Necronomicon, based on a letter from HPL to CAS (11/18/30). If so, William Beckford's Vathek may also be connected to the Mythos.
• The Weaver in the Vault, Weird Tales, Vol. 23, No. 1, January 1934. Mentions Zothique; (Grey Weavers); Tasuun; Chaon Gacca; Xylac; Yuckla; Yoros; Zul-Bha-Sair; Weaver; Famorgh; Lunalia; Miraab.
• The Witchcraft of Ulua, Weird Tales, Vol. 23, No. 2, February 1934. Mentions Tasuun; Zothique; Famorgh; Lunalia; Ulua; Dooza Thom.
• The Charnel God, Weird Tales, Vol. 23, No. 3, March 1934. Mentions Zothique; Zul- Bha-Sair; Mordiggian; Ghouls; Xylac; Yoros; Tasuun.
• The Death of Malygris, Weird Tales, Vol. 23, No. 4, April 1934. Mentions Poseidonis; Malygris; Susran; Atlantis; Taaran.
• The Tomb-Spawn, Weird Tales, Vol. 23, No. 5, May 1934. Mentions Zothique; Yoros; Ossaru; Thasaidon; Nioth Korghai; Cincor; Namirrha; Tasuun; Ustaim; Ghorii.
• The Muse of Hyperborea, The Fantasy Fan, June 1934. Mentions Hyperborea.
• The Colossus of Ylourgne, Weird Tales, Vol. 23, No. 6, June 1934. Mentions Averoigne, France; du Nord, Gaspard; Vyones, France; Nathaire; Ylourgne; Isoile; La Frênaie, France; Ximes, France; Perigon; Sainte Zenobia, France.
• The Epiphany of Death, The Fantasy Fan, July 1934. Mentions Ptolemides; Hyperborea; Mu; Atlantis.
• The Disinterment of Venus, Weird Tales, Vol. 24, No. 1, July 1934. Mentions Averoigne, France; Perigon; Sainte Zenobia; Vyones, France.
• The Seven Geases ^{1 2}, Weird Tales, Vol. 24, No. 4, October 1934. Mentions Abhoth; Atlach-Nacha; Haon-Dor; Hyperborea; Serpent-People; Voormithadreth, Mt.; Commoriom; Saturn; (Great) Old Ones; Archetypes; Eiglophian Mountains; Tsathoggua; Voormis.
• Xeethra, Weird Tales, Vol. 24, No. 6, December 1934. Mentions Carnamagos; Zothique; The Testaments of Carnamagos; Xeethra; Thasaidon; Cincor; Calyz; Sha-Karag.
• The Dark Eidolon, Weird Tales, Vol. 25, No. 1, January 1935. Mentions Xylac; Thasaidon; Hyperborea; Mu; Poseidonis; Tasuun; Yoros; Zul-Bha-Sair; Mordiggian; Tinarath; Uccastrog; Cyntrom; Thamogorgos; Namirrha; Ummaos; Naat; Sotar; (Aforgomon?); Xeethra; Zothique.
• The Last Hieroglyph, Weird Tales, Vol. 25, No. 4, April 1935. Mentions Ummaos; Vergama; Xylac; Yoros; Zul-Bha-Sair; Zothique.
• The Flower-Women, Weird Tales, Vol. 25, No. 5, May 1935. Mentions Xiccarph; Maal Dweb; Athlé; Mornoth; Ulassa; Nouph; Rhul; Votalp; Ispazars.
• The Treader of the Dust, Weird Tales, Vol. 26, No. 2, August 1935. Mentions Carnamagos; Quachil Uttaos; The Testaments of Carnamagos.
• Vulthoom, Weird Tales, Vol. 26, No. 3, September 1935. Mentions Aihais; Mars; Vulthoom; Ignarh-Vath; Ravormos; Ta-Vho-Shai; Ignarh.
• The Chain of Aforgomon, Weird Tales, Vol. 26, No. 6, December 1935. Mentions Aforgomon; Atlantis; Kalood; Hestan; Xexanoth.
• The Black Abbot of Puthuum, Weird Tales, Vol. 27, No. 3, March 1936. Mentions Ilcar; Izdrel; Ojhal; Yoros; Zothique.
• Necromancy in Naat, Weird Tales, Vol. 28, No. 1, July 1936. Mentions Zothique; Sha-Karag; Naat; Xylac.
• The Death of Ilalotha, Weird Tales, Vol. 30, No. 3, September 1937. Mentions Ludar; Ludar's Litany to Thasaidon; Tasuun; Thasaidon; Zothique.
• The Garden of Adompha, Weird Tales, Vol. 31, No. 4, April 1938. Mentions dedaim; Ludar; Ludar's Litany to Thasaidon; Sotar; Thasaidon; Zothique.
• Mother of Toads, Weird Tales, Vol. 32, No. 1, July 1938. Mentions Averoigne, France; Les Hiboux, France.
• The Coming of the White Worm ^{1 2}, Stirring Science Stories, April 1941. Mentions Eibon; Evagh; Hyperborea; Mhu Thulan; Rlim Shaikorth; Cerngoth; Pnom; Exorcisms of Pnom; Yarak; (Great) Old Ones; Yikilth; Thulask; Polarion; Leqquan; Aguil; (Book of Eibon).
• The Enchantress of Sylaire, Weird Tales, Vol. 35, No. 10, July 1941. Mentions Averoigne, France; Druids; Isoile; Sephora; Werewolves.
• The Family Tree of the Gods, The Acolyte, No. 7, Summer 1944. Mentions Tsathoggua; Parchments of Pnom; Pnom; Elder Script; Azathoth; Hziulquoigmnzhah; Ghizguth; Cxaxukluth; Knygathin Zhaum; Voormis; Commoriom; Ech-Pi-El; Cthulhu; Zstylzhemgni; Yuggoth; Yaksh (Neptune); Cykranosh (Saturn); N'kai; Yoth; K'n-yan; Zamacona y Nuñez, Pánfilo de; Ycnagnnisssz; Zoth; Shathak; Zvilpogghua; Sfaticllp.
• The Master of the Crabs, Weird Tales, Vol. 40, No. 3, March 1948. Mentions Zothique; Naat; Iribos; dedaim; Basatan.
• Zothique, in The Dark Chateau and Other Poems, Sauk City, WI: Arkham House, 1951. Poem. Mentions Zothique.
• Morthylla, Weird Tales, Vol. 45, No. 2, May 1953. Mentions Lamias; Morthylla; Psiom; Umbri; Zothique.
• An Offering to the Moon, Weird Tales, Vol. 45, No. 4, September 1953. Mentions Mu; Rhalu.
• Tolometh, in Spells and Philtres, Sauk City, WI: Arkham House, 1958. Poem. Mentions Poseidonis; Tolometh.
• The Theft of Thirty-Nine Girdles (as The Power of Hyperborea), Saturn Science Fiction and Fantasy, March 1958. Mentions Hyperborea; Satampra Zeiros; Uzuldaroum; Leniqua.
• Atlantis, in Selected Poems, Sauk City, WI: Arkham House, 1971. Poem. Mentions Atlantis.
• In Lemuria, in Selected Poems, Sauk City, WI: Arkham House, 1971. Poem. Mentions Lemuria.
• Ascharia (as Asharia), Crypt of Cthulhu, No. 27, Hallowmas 1984. Outline and fragment. Mentions Ascharia; Lemuria; Mhaggalok (Jupiter?); Mhuth (Mars?); Mu; Roiba (Venus?).
• The House of Haon-Dor, Crypt of Cthulhu, No. 27, Hallowmas 1984. Fragment. Mentions Haon-Dor.
• Shapes of Adamant, Crypt of Cthulhu, No. 27, Hallowmas 1984. Fragment. Mentions Avandas; Dooza Thom; Nooth-Kemmor; Poseidonis; Zothique.
• Mandor's Enemy, Crypt of Cthulhu, No. 27, Hallowmas 1984. Fragment. Mentions Famorgh; Tasuun; (Zothique).
• The Sorceress of Averoigne/The Tower of Istarelle, Crypt of Cthulhu, No. 27, Hallowmas 1984. Synopsis for unwritten story. Mentions Averoigne, France; Vyones, France.
• The Feet of Sidaiva, Crypt of Cthulhu, No. 27, Hallowmas 1984. Synopsis for unwritten story. Mentions Ummaos; Zothique; Zylac, Zothique (Xylac).
• Queen of the Sabbat, Crypt of Cthulhu, No. 27, Hallowmas 1984. Synopsis for unwritten story. Mentions Averoigne, France; La Frênaie, France.
• The Hyperborean City, Crypt of Cthulhu, No. 27, Hallowmas 1984. Synopsis for unwritten story. Mentions Hyperborea.
• The Werewolf of Averoigne, Crypt of Cthulhu, No. 27, Hallowmas 1984. Synopsis for unwritten story. Mentions Averoigne, France; Werewolves.
• The Rebirth of the Flame, Crypt of Cthulhu, No. 27, Hallowmas 1984. Synopsis for unwritten story. Mentions Angarth, (Giles); Hastane, (Philip); Singing Flame; Ydmos.
• Conclusion to The Return of the Sorcerer, Klarkash-Ton, No. 1, June 1988. Original ending. No direct Mythos mentions.
• The Music of Death, in Strange Shadows: The Uncollected Fiction and Essays of Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Outline and fragment. Mentions Hastane, Philip.
• The Infernal Star, in Strange Shadows: The Uncollected Fiction and Essays of Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Fragment. Mentions Antillia; Atlantis; Avalzant; Averoigne, France; Carnamagos; Cimmeria; Eibon; Ghooric Zone; Hali [prophet]; Hyperborea; Lomar; Mhu Thulan; Moaria; Mordiggian; Necronomicon; Pandemonium; Pnidleethon; Poseidonis; Psollantha; The Testaments of Carnamagos; Thilil; Vermazbor; Vertnain; Yamil Zacra; Yuzh; Zothique.
• Mnemoka, in Strange Shadows: The Uncollected Fiction and Essays of Clark Ashton Smith, Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Fragment. Mentions Aihais; Ignarh-Vath; Mars.
• The Fugitives, in Strange Shadows: The Uncollected Fiction and Essays of Clark Ashton Smith, Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Play fragment. Mentions Alnlephrom; Poseidonis.
• I Am a Witch, in Strange Shadows: The Uncollected Fiction and Essays of Clark Ashton Smith, Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Synopsis for unwritten story. Mentions Arkham, MA.
• The Galley from Atlantis, in Strange Shadows: The Uncollected Fiction and Essays of Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Synopsis for unwritten story. Mentions Atlantis.
• Poseidon, in Strange Shadows: The Uncollected Fiction and Essays of Clark Ashton Smith, Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Synopsis for unwritten story. Mentions Atlantis.
• The Dead Will Cuckold You, in Strange Shadows: The Uncollected Fiction and Essays of Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Play. Mentions Faraad; Ililot; Mumba Vut; Thasaidon; Yoros; Zothique.
• In the Book of Vergama, in Strange Shadows: The Uncollected Fiction and Essays of Steve Behrends with Donald Sidney-Fryer and Rah Hoffman, ed., Westport, CT: Greenwood Press, Inc., 1989. Unpublished preface to "The Last Hieroglyph". Mentions Cincor; Naat; Vergama; Xylac; Zothique.

Footnotes

• Cthulhu Mythos story acording to Clark Ashton Smith in H.P.L: Memoirs, Critiques, Biographies SSR Publications 1955
• Cthulhu Mythos story according to Lin Carter in Baleful Myths and Liturgies: Clark Ashton Smith's Contribitions to the Cthulhu Mythos In Dark Eidolon 3. Necronomicon Press