Answer: I suspect you've discovered some moisture ants. This ant gets its common name of cornfield ant from its close association with the corn root aphid, and because of their structural nesting habit of utilizing high moisture areas. It is found throughout much of the lower mainland.
Workers are about 1/16-1/8" long; queens about 1/4" long. Color is brown to very dark reddish brown, approaching black. Antenna 12-segmented, without a Workers capable of emitting a strong formic-acid odor. Mature colonies are moderate to large, apparently composed of up to several thousand workers but only one queen. If mounds are present, they range up to 8-10". Developmental time (egg to adult) averages about 88 days (range 59-127 days). Reproduction is present in the colony from midsummer to autumn, with mating apparently occurring in the nest before swarming. Swarms usually occur July through September and may be composed of males and/or females. Queens burrow into a chamber and usually do not lay eggs until the following spring. Queens may live more than 10 years.
If this doesn't match the description of the ants you've found, try the following website. It has lots of pictures and descriptions of the most commonly encountered ants:
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