Changes in pottery decoration and vessel shape help identify when the Gull Lake mounds were built and what prehistoric group lived there by comparing Gull Lake pottery with dated regional pottery sequences. Because some later prehistoric pottery types in that sequence are associated at other sites with early historic artifacts, archaeologists connect those types to the early history of the area and identify the Dakota people as makers of much of the late-prehistoric pottery in the headwaters region, suggesting the people at Gull Lake may have been ancestral Dakota. The only complete pottery vessel found in the Gull Lake excavations, and believed to be the only one intentionally buried with an individual, is about 7 1/2 inches tall and has a net impressed surface with two parallel bands and oblique lines of cord-wrapped-stick impressions around its upper portion. Most Woodland pottery was made by mixing clay with crushed rock or sand temper, shaping the vessel, sometimes adding decoration before drying, and firing it in an open fire so it would not soften in water; surface patterns on sherds also show how a vessel was formed, including net impressed pottery possibly made with a net or net-like bag and cord impressed pottery shaped with a cord-wrapped paddle. Pottery sherds found mostly in mound fill suggest a maximum age for mound construction, since a mound was probably not built before the pottery types in its fill were in use. Three main pottery types are represented: Brainerd, most frequently found in the mound fill, usually net impressed and sometimes marked with small punctates, cord-wrapped stick impressions near the rim, or distinctive single cord impressions; it was first defined during the Gull Lake Mound excavations, once dated to about A.D. 600 to A.D. 800, but some researchers now believe it was used as early as 600 B.C., a view supported by recent radiocarbon dates from food residue inside the Gull Lake vessel. St. Croix is generally cordmarked pottery with distinctive dentate stamped decoration near the rim and was used in the late-Middle Woodland period between A.D. 600 and A.D. 800. Malmo is a smooth surface ware often marked near the rim with incised lines, punctates, or bosses and was used during the Middle Woodland period between 800 B.C. and A.D. 500.