The papers of Rev. W. O. Evans can be divided into sermons, ca 1891 - 1923; addresses on subjects closely related to religion, ca 1905 - 1923; sermon text books, 1882 - 1919; journals 1909 - 1920; hymns and translations of hymns from English to Welsh; material on the history of Wesleyanism in the Portmadoc area such as newspaper cuttings, letters, essays, 1870 - ca 1936; miscellaneous material which consist of addresses, letters, notes and scrapbooks, 1882 - 1981. There is also a virtually unbroken series of diaries, 1882 - 1933.
The Gwyllt y Mynydd material contains diaries which range from 1855 - 1908 along with essays, articles, sermons and poetry. Also included is a collection book of the Edward Jones Memorial Chapel, Bathafarn, Rhuthun, Denbighshire, 1778 - 1837 and detailed notes of the work of Rev. W.H. Evans at the circuit of Abergele, 1860 - 1861 and Llanfair Caereinion, 1863. Amongst the correspondence are his letters to his mother, 1860 - 1861.
There are a few works of poetry by Cynfaen, 1851 - 1877 and a diary, 1855 and sermons, notes and poetry belonging to Ioan Tachwedd, including a copy drawing of his home, Bryn Rhedydd, Ysgeifiog, Flintshire.
There is a group of correspondence between all family members and notebooks with pedigrees and notes on family history.