jQuery Grid Plugin - jqGrid

I need to swap out between 2 grid definitions. My code below does set the swapped "url" property, but does not change "caption", "colNames", "colModel" etc...

load_table() is fired with an onchange for the select input that chooses which grid definition is desired.

What am I doing wrong?

var grids = {
          one: {
                caption: 'Switch Test One',
                url: 'switch.cgi?q=1',
                datatype: 'json',
                mtype: 'GET',
                colNames:['id', 'One'],
                colModel: [{name: 'id'}, {name: 'one'}],
                height: '200px',
                imgpath: 'css/jqgrid/steel/images',
               },
          two: {
                caption: 'Switch Test Two',
                url: 'switch.cgi?q=2',
                datatype: 'json',
                mtype: 'GET',
                colNames:['id', 'Two'],
                colModel: [{name: 'id'}, {name: 'two'}],
                height: '200px',
                imgpath: 'css/jqgrid/steel/images',
               },
};

jQuery(document).ready(function(){
    jQuery("#switch_grid").jqGrid( grids['one'] );
});

function load_table () {
    var which = $('#switch').val(); // get value from select dropdown
    jQuery("#switch_grid").setGridParam(grids[which]).trigger('reloadGrid');
}