There are two original series in the collection, Correspondence Received and Other Documents. The correspondence consists of letters received by Hasselborg. It also includes telegrams as well as acknowledgment of gifts of specimens he donated or sold to the Museum of Vertebrate Zoology at the University of California at Berkeley. Other documents include journals kept on hunting trips, weather journals, a brief trapping journal, licenses issued to Hasselborg, newspaper clippings, photographs, and miscellany. These two series cover the period from 1907-1955.

With the addition of accession no. 96-36 a third series, Correspondence Sent, was added in 1996. This series primarily contains letters and postcards written by Hasselborg to his sisters Flora and Ebba. It also contains a few letters written to his mother and other family members. In 1954-1955 there is a sub-series of letters between Ebba and Flora. The Hasselborg sisters’ letters were primarily about Allan Hasselborg’s condition and whereabouts after he left his Mole Harbor homestead in 1954. This series also includes the John Holzworth book The Wild Grizzlies of Alaska, annotated by Hasselborg, a few newspaper clippings, and photographs of bears. To retain the provenance of this accession, these items are included with the correspondence in the third series.

With accession no. 96-42, a fourth series, Correspondence with Museum of Vertebrate Zoology, University of California, Berkeley, was added to Ms 2. These letters were written by Hasselborg to various Museum staff members from 1909 to 1937 and document his activities during this time period.

Accession no. 2005-028 and 2012-003 total 13 folders which include photographs, negatives, and interviews collected during the research for the book Bear Man of Admiralty Island: A Biography of Allen E. Hasselborg by John Howe.