Thanks Robert and Ken. I'm seeing light at the end of the tunnel. Now I'm getting a TypeError that refers back to the geometryEngine saying "c.getCacheValue is not a function". I'm assuming I may have the wrong references (currently referencing 3.13)?
var geoms = [];
pondLayer.queryFeatures(query, function(featureSet){
for (var i = 0; i < featureSet.features.length; i++) {
var feature = featureSet.features;
geoms.push(feature);
};
var union = geometryEngine.union(geoms); //Notice I am using geometryEngine and not geometryEngineAsync
var query2 = new Query();
query2.geometry = union;
query2.spatialRelationship = Query.SPATIAL_REL_CONTAINS;
pondLayer.selectFeatures(query2, FeatureLayer.SELECTION_NEW);
});