In this poem, Clark Ashton Smith (CAS) name checks Charles Baudelaire, and indeed these lines murmur with the dark magic of that notorious French poet.
In the second stanza, the narrator speaks of quoting Baudelaire, and although the specific source is not named, I assume he is referring to "Recueillement" (poem CIV from the 1868 edition of Les Fleurs du mal). That poem has most frequently been translated into English with the title "Meditation", although when CAS himself translated it into prose, he used the title "Contemplation".
Although I'm partial to Robert Lowell's English translation of "Recueillement", the opening of CAS' own rendering of the same poem is worth quoting:
Be wise, my Sorrow, and be tranquil; thou woulds't reclaim the evening; it descends; behold: an obscure atmosphere envelopes the city, bearing peace to some and care to others.
The uneasy mood of that opening permeates the early stanzas of "Nocturne: Grant Avenue":
I saw your face by subtler dreams illumed,
And heard you speak
Of how, amid that multifold parterre,
Beauty and mystery and evil softly bloomed.
The conflict between the commonplace dreariness of the populated town and the bucolic joys found "When all the forest fountains sang unheard of us" underlies this poem, and the apogee occurs when the lovers find they can retain the essence of the latter even when they find themselves walled in by the former:
And, through the city's glare and sound,
What ghosts of faint hesternal flowers blew
And freshness home from woodlands far away:
At parting in your long, deep kiss I found
The savor of sweet balm and spiced immortal bay.
CAS wrote many poems of love built around memories of pastoral trysts, but "Nocturne: Grant Avenue" stands out from the pack for its subtle use of a "tension of place" that masterfully invokes the spirit of Baudelaire.