What is the lowest GNIS Feature ID from County of sheridan?
CREATE TABLE "united_states" (
  "name" text,
  "gnis_feature_id" real,
  "state" text,
  "county" text,
  "type" text,
  "usgs_7_5_map" text
);
SELECT MIN("gnis_feature_id") FROM "united_states" WHERE "county"='sheridan';