Oro Lake Regional Park
Note the stem is covered with rounded projections called tubercles. Spines arise from an area at the apex of each tubercle called the areole. There are 3-4 (uncommonly more) central spines pointing more or less at right angles to the surface, and 12 to 40 radial spines pointing more or less parallel to the surface.
Each tubercle has a groove on the upper side. The flower/fruit is borne at the base of the groove.
Mamillaria/Coryphantha: Note that Budd's Flora places this species in genus Mamillaria, while Flora of Alberta places it in genus Coryphantha. The following are the answers to the key questions in these flora that lead to Mamillaria or Coryphantha.
Cactaceae: Answers to key questions in Budd's Flora leading to this family.