Pollen analysis of a 96 cm core from Soda Lake, San Luis Obispo County, California, documents the invasion of exotic plants and the transformation of native grassland following settlement of the area. Exotic types include Eucalyptus (Australian gum), Ulmus (elm), Salsola (tumble weed), Cereale, Zea, and Erodium cicutarium. Grass and Linanthus pollen is less abundant during the historic period, and the pollen of Chenopodiaceae-Amaranthus and Eriogonum is more abundant. In part, these values reflect the replacement of native bunch grass by introduced weeds, but the increased Chenopodiaceae-Amaranthus percentages may also reflect the expansion of halophytic vegetation near the lake, and the increased percentages of Ruppia indicates greater salinity in the last few years. In contrast, freshwater conditions existed prior to settlement.

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