A nice example of how helpful a quick ANNIE search can be. I took the phrase 'day of the dead' and ran it through as a W (keyword) search. 'of' and 'the' are not indexed, but of the 19 items with both 'day' and 'dead' 3 are immediately and obviously useful: 
 
 You searched for the KEYWORD: day of the dead          W&L CATALOG
 19 entries found, entries 1-8 are:                     LOCATIONS
     1  The day of the dead : tradition and change in c LEYBURN
     2  Dubliners,                                      LEYBURN
     3  Easy in the islands : stories                   LEYBURN
     4  The Egyptian Book of the dead : the Book of goi LEYBURN
     5  Halloween and other festivals of death and life LEYBURN
     6  Hope should always, stories                     LEYBURN
     7  Innocent blood crying to God from the streets o LEYBURN
     8  Joyce: a collection of critical essays,         LEYBURN
     9  The judgment of the dead: the idea of life afte LEYBURN
    10  Let the dead bury their dead : and other storie LEYBURN
    11  Names of horses                                 LEYBURN
    12  The poetry and voice of Ted Hughes.             LEYBURN
    13  The powers that prey,                           LEYBURN
    14  Redefining the American Gothic : from Wieland t LEYBURN
    15  Selections.                                     LEYBURN
    16  The skeleton at the feast : the Day of the Dead LEYBURN
    17  The stories of Breece D'J Pancake               LEYBURN
    18  Todos Santos in rural Tlaxcala : a syncretic, e LEYBURN
    19  Xanadu 2    

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 AUTHOR       Carmichael, Elizabeth.
 TITLE        The skeleton at the feast : the Day of the Dead in Mexico /
                Elizabeth Carmichael, Chloe Sayer.
 EDITION      1st University of Texas Press ed.
 PUBLISHER    Austin : University of Texas Press, 1992.
 DESCRIPT     160 p., 32 p. of plates : ill. (some col.), map ; 28 cm.
 NOTE         "Published in co-operation with British Museum Press."
 BIBLIOG.     Includes bibliographical references (p. 153-155) and index.
 SUBJECT      All Souls' Day --Mexico.
              Festivals --Mexico.
              Dead --Folklore.
              Mexico --Social life and customs.
 Leyburn Library        GT4995.A4 C37 1992      


 AUTHOR       Hernandez, Joanne Farb.
 TITLE        The day of the dead : tradition and change in contemporary Mexico
                : Triton Museum of Art, October 28 through November 25, 1979 =
                El dia de los muertos : su tradicion, su cambio en un Mexico
                contemporaneo / Joanne Farb Hernandez and Samuel R. Hernandez ;
                [photography on location, Sam Hernandez ; studio photography,
                Mike Narciso ; translation, Carmen Garcia]
 PUBLISHER    [Santa Clara, Calif.] : The Museum, [1979]
 DESCRIPT     45 p. : ill. (some col.) ; 24 cm.
 NOTE         English and Spanish.
 BIBLIOG.     Bibliography: p. 44-45.
 SUBJECT      Dead --Folklore --Mexico --Exhibitions.
 Leyburn Library        GR115 .H47
I originally found the next one with another search, though it's number 18 above. The 'tl' in 'Tlaxcala' is the same consonant cluster as in 'Tepoztlan, for a very good reason... 
 You searched for the KEYWORD: todos santos                  W&L CATALOG
 
 AUTHOR       Nutini, Hugo G.
 TITLE        Todos Santos in rural Tlaxcala : a syncretic, expressive, and
                symbolic analysis of the cult of the dead / Hugo G. Nutini.
 PUBLISHER    Princeton, N.J. : Princeton University Press, c1988.
 DESCRIPT     xv, 471 p. ; 24 cm.
 BIBLIOG.     Bibliography: p. 445-454.
 NOTE         Includes index.
 SUBJECT      Nahuas --Religion and mythology.
              Indians of Mexico --Tlaxcala (State) --Religion and mythology.
              All Saints' Day.
              All Souls' Day.
              Nahuas --Acculturation.
Leyburn Library        F1221.N3 N895 1988
These sources could be useful if you need some background on the festival which is the setting for the poem.