“Dyke” (meaning “lesbian”) comes from the word “bulldyke.” “In American homosexual argot, female inverts, or lesbian lovers, are known euphemistically as ‘bulldykers,’ whatever that may mean: at least that is their sobriquet in the ‘Red Light’ district of Philadelphia” was printed in the book Human Sexuality: A Medico-literary Treatise on the Laws, Anomalies, and Relations of Sex (1906)by Joseph Richardson Parke.
 
However, most sources are from New York City. “She stated that she had indulged in the practice of ‘bull diking,’ as she termed it” was printed by a New York City doctor in Medical Review of Reviews in August 1921. “That’s what we calls bulldyker in Harlem” (lesbian) was printed in the novel Home to Harlem by Claude McKay. “This is particularly true among the few inmates who turn out to be bulldykes instead of femmes” was printed in the book Hellhole:
The Shocking Story of the Inmates and Life in the New York City House of Detention for Women (1967) by Sara Harris. “Several of the gay (homo) Greenwich Village bars have their female opposites (bulldikes) as bouncers” was printed in the syndicated “Voice of Broadway” column by Jack O’Brian in many newspapers on May 4, 1968.
 
The origin of “bulldyke” is unknown. It perhaps comes from mining, where these terms are defined in this Glossary of Mining Terms:
 
Bull quartz - A prospector’s term for white, coarse-grained, barren quartz.
Dyke - A long and relatively thin body of igneous rock that, while in the molten state, intruded a fissure in older rocks.
 
 
Wikipedia: Dyke (slang)
The term dyke or dike is a slang noun meaning lesbian; it is also a slang adjective describing things associated with lesbianism. It originated as a homophobic and misogynistic slur for a masculine, butch, tomboyish, or androgynous female. While pejorative use of the word still exists, the term dyke has been reappropriated by out and proud lesbians as a word implying assertiveness and toughness, or simply as a neutral synonym for lesbian.
 
Origins
The origin of the term is obscure and many theories have been proposed. The Oxford English Dictionary notes the first attestation as Berrey and Van den Bark’s 1942 American Thesaurus of Slang. There, dike was the more common term. From the mid-19th century to the early 20th century, dike had been American slang for a well-dressed man, with “diked out” and “out on a dike” indicating a young man was in his best clothes and ready for a night on the town. The etymology of that term is also obscure, but may have originated as a Virginian variant of deck and decked out.
 
However, the term bulldyker preceded dyke in print, appearing in Harlem Renaissance novels in the 1920s. Claude McKay’s 1928 Home to Harlem includes the passage that lesbians are “what we calls bulldyker in Harlem… I don’t understan’... a bulldyking woman.” From the context in the novel, the word was considered crude and pejorative at the time. This may be related to the late-19th-century slang use of dike (“ditch”) for the vulva. Bull (“male cattle”) being used in the sense of “masculine” and “aggressive” (e.g., in bullish), a bulldyke would have implied (with similar levels of offensiveness) a “masculine cunt”.
 
(Oxford English Dictionary)
bull dyke, n.
A lesbian, esp. one whose appearance, behaviour, or identity is regarded as masculine. Also: any woman who is regarded as masculine in some way. Cf. dyke n.
Sometimes spec. in the context of a lesbian relationship: a partner who takes on a more dominant or active role, either sexually or in a more general sense. Cf. stud n.2 7c.
1931   Broadway Brevities Weekly 31 Aug. 10/2 (heading)  Bulldykes Rendezvouz [sic]. Women of good class have their private clubs… Men not admitted to Club Mali and Igel, the biggest. Some gotten up mannishly but most..dress conventionally enough.
1942   L. V. Berrey & M. Van den Bark Amer. Thes. Slang §405/3   Masculine woman, boy, bulldike, bulldyke, bulldiker.
1964   J. Rechy City of Night 174   On the dance-floor, too, lesbians—the masculine ones, the bulldikes—dance with hugely effeminate queens.
       
Google Books
Human Sexuality:
A Medico-literary Treatise on the Laws, Anomalies, and Relations of Sex
By Joseph Richardson Parke
Philadelphia, PA: Professional Publishing Company
1906
Pg. 309:
In American homosexual argot, female inverts, or lesbian lovers, are known euphemistically as “bulldykers,” whatever that may mean: at least that is their sobriquet in the “Red Light” district of Philadelphia.
 
Google Books
August 1921, Medical Review of Reviews, “The ‘Fairy’ and the Lady Lover” by Perry M. Lichtenstein, M.D. (Physician in House of Detention, New York), pg. 373:
She stated that she had indulged in the practice of ‘bull diking,’ as she termed it. She was a prisoner in one of the reformatories, and there a certain young woman fell in love with her.
 
Google Books
Home to Harlem
By Claude McKay
New York, NY: Harper & Brothers
1928
Pg. 129:
“Sapphic and Lesbian…beautiful words.”
 
“What is that there Leshbian?”
 
”...Lovely word, eh?”
 
“That’s what we calls bulldyker in Harlem,” drawled Jake^ “Them’s all ugly womens.”
 
“Not all. And that’s a damned ugly name,” the waiter said. “Harlem is too savage about some things. Bulldyker,” the waiter stressed with a sneer.
   
Jake grinned. “‘But tha’s what they is, ain’t it?”
 
He began humming:
 
“And there is two things in Harlem I don’t understan’
It is a bulldyking woman and a faggoty man….”
   
31 March 1928, Pittsburgh (PA) Courier, “Ferris Scores Obscenity In Our Literature” by William H. Ferris, A. M.,  second sec., pg. 8, col. 4:
Then comes Claude McKay, who goes Van Vechten and Hughes one better. (...) Then he uses phrases like “bull diker,” which are only bar-room terms.
   
Google Books
Hot News
By Emile Gauvreau
New York, NY: Macaulay Company
1931
Pg. 187:
The opening bars would ring in my ears the next day while my presses roared:
 
“Two kinds of people I can’t stan’
“Is a bulldyking woman and a pansy man.”
       
Google Books
Pinktoes, a novel
By Chester B. Himes
New York, NY: G.P. Putnam’s Sons
1965
Pg. 16:
But being as nothing happened, someone said finally, Them cats ain’t fighting, them cats is just loving, them is fairy cats, or else they is bulldiking.
 
Google Books
Hellhole:
The Shocking Story of the Inmates and Life in the New York City House of Detention for Women
By Sara Harris
New York, NY: Dutton
1967
Pg. 201:
This is particularly true among the few inmates who turn out to be bulldykes instead of femmes. Some of them, like twenty-nine-year-old Florence Somers, actually “discover” themselves in the jail.
 
4 May 1968, Shenandoah (PA) Evening Herald - Ashland (PA) Daily News, “Voice of Broadway” by Jack O’Brian, pg. 2, col. 8:
Several of the gay (homo) Greenwich Village bars have their female opposites (bulldikes) as bouncers.