The designer looked to the same Spanish, Mexican and Moroccan influences that define the wider Downtown LA Proper, such as terracotta Roman clay plaster walls and ceilings when conceptualising the bar.
"The warm, earthy tones of the lounge are in concert with the larger hotel while striking their own note entirely," said Wearstler.
"Dahlia feels like it has been there for ages," added the designer, who has been named as a judge for the inaugural Dezeen Awards China.
Visitors enter the bar through yellow-tinged stained glass doors that were custom-made for the venue by Los Angeles' historic Judson Studios, which claims to be the oldest family-run stained glass company in America.
Seating was created from a mix of built-in reddish banquettes and low-slung curved armchairs that hug circular timber tables, while a geometric chandelier draped in light-filtering silk was suspended overhead.
In one corner, an embossed and low-slung black cabinet supports two squat table lamps that look like oversized green olives.
Wearstler adorned the clay plaster walls with a mishmash of vintage and contemporary textural artwork, which was finished in ceramic and sand. Various local artists were included in the mix.
Defined by "saturated hues and dramatic lighting," the cocktail lounge also features a bar clad with lilac-hued Moroccan cement tiles and woven crimson rugs.
"This is the kind of space where you can entirely lose track of time," said the designer.
Known for her distinctively eclectic style, Wearstler has created interiors for various other destinations that are part of the Proper Hotel Group. The designer scoured vintage shops to source the furniture that decorates the living room-style lobby of a Santa Monica branch while an Austin location features a sculptural oak staircase that doubles as a plinth for Wearstler's own glazed earthenware pots and vases.
The photography is by The Ingalls.