Stone Mortar

A stone mortar is a portable block, boulder or cobble with a deep pit worked into its upper surface for pounding with a pestle. The simplest are unshaped boulders with a parabolic pit; shaped forms include globular bowl mortars, thin-walled sandstone bowls, and heavy conical and cylindrical blocks, some with a pointed underside for setting in the ground (Holmes 1919; Hodge 1907; Glassow 1996). In the East most are sandstone blocks or slabs with a round cavity on one or both faces (Fowke 1896).

The pit was pecked out with hammerstones. Mortars from the California desert and islands show a faster method: a ring-shaped groove was pecked to isolate a central plug, which was then knocked out with a single blow. In experiments, hollowing 215 cc of sandstone took 37,200 blows over about 12.75 hours (Schneider and Osborne 1996).

Mortars were set in the ground for stability, sometimes with a bottomless basket set on the rim as a hopper (Hodge 1907). Kroeber (1925) records that California mortars and pestles were used mainly for acorns and metates for small seeds, but ethnographies also list bulrush roots, mesquite beans, meat, bone, paint and tobacco (Glassow 1996; Hodge 1907). The key trait is a deep, smoothed pounding pit in a stone that can be lifted and moved.

From small paint cups to basins holding several gallons (Hodge 1907). A Petaluma, California, collection held mortars up to about 610 mm across and 34–45 kg in weight (Moorehead 1910, converted from feet and pounds); unfinished California blanks measure 260–450 mm in diameter (Schneider and Osborne 1996). A small Columbia River basalt mortar at the Metropolitan Museum is 73 mm high and 93 mm across.

California has the greatest number and variety; mortars are also common in the Great Basin, the Columbia Plateau and the Southwest, including southern Arizona (Hodge 1907; Glassow 1996; Schneider and Osborne 1996; Nevada Rock Art Foundation 2015). Smaller numbers occur across the East, mostly as sandstone blocks and slabs from Tennessee, Ohio, West Virginia, North Carolina, Mississippi, Arkansas and Iowa (Fowke 1896), and carved tobacco mortars are known from the Northwest Coast (Hodge 1907).

Identification tips: Check that the pit is smooth and rounded from pounding and that the block is small enough to move. Eastern mortars often have a cavity on both faces.

Similar types: A bedrock mortar is a pit worn into an outcrop and cannot be moved. A Nutting Stone has several small, shallow cup-shaped pits rather than one deep basin. A Metate (Grinding Stone) has a broad flat or troughed surface worn by back-and-forth rubbing. A Steatite Bowl is a thin-walled carved soapstone vessel; Hodge (1907) did not class such vessels as mortars.

Naming: A hopper mortar is a flat slab or shallow mortar topped with a bottomless basketry hopper; in the Chumash area the hopper was fixed on with asphalt (Kroeber 1925).

Dating evidence: At CA-SBA-53 on the Goleta Slough, 69 mortars came from deposits dated 4,980–4,620 B.P.; these are barely shaped boulders, while globular bowl mortars and hopper mortars appear after about 4,500 B.P. (Glassow 1996).