add_filter( 'tribe-events-bar-filters',  'setup_my_field_in_bar', 1, 1 );

function setup_my_field_in_bar( $filters ) {
    $filters['tribe-bar-my-field'] = array(
        'name' => 'event_state',
        'caption' => 'State',
        'html' => '<select name="event_state" id="event_state">
                        <option selected="selected" disabled value="">Select Your State</option>
                        <option value="Alabama">Alabama</option>
                        <option value="Alaska">Alaska</option>
                        <option value="Arizona">Arizona</option>
                        <option value="Arkansas">Arkansas</option>
                        <option value="California">California</option>
                        <option value="Colorado">Colorado</option>
                        <option value="Connecticut">Connecticut</option>
                        <option value="Delaware">Delaware</option>
                        <option value="District Of Columbia">District Of Columbia</option>
                        <option value="Florida">Florida</option>
                        <option value="Georgia">Georgia</option>
                        <option value="Hawaii">Hawaii</option>
                        <option value="Idaho">Idaho</option>
                        <option value="Illinois">Illinois</option>
                        <option value="Indiana">Indiana</option>
                        <option value="Iowa">Iowa</option>
                        <option value="Kansas">Kansas</option>
                        <option value="Kentucky">Kentucky</option>
                        <option value="Louisiana">Louisiana</option>
                        <option value="Maine">Maine</option>
                        <option value="Maryland">Maryland</option>
                        <option value="Massachusetts">Massachusetts</option>
                        <option value="Michigan">Michigan</option>
                        <option value="Minnesota">Minnesota</option>
                        <option value="Mississippi">Mississippi</option>
                        <option value="Missouri">Missouri</option>
                        <option value="Montana">Montana</option>
                        <option value="Nebraska">Nebraska</option>
                        <option value="Nevada">Nevada</option>
                        <option value="New Hampshire">New Hampshire</option>
                        <option value="New Jersey">New Jersey</option>
                        <option value="New Mexico">New Mexico</option>
                        <option value="New York">New York</option>
                        <option value="North Carolina">North Carolina</option>
                        <option value="North Dakota">North Dakota</option>
                        <option value="Ohio">Ohio</option>
                        <option value="Oklahoma">Oklahoma</option>
                        <option value="Oregon">Oregon</option>
                        <option value="Pennsylvania">Pennsylvania</option>
                        <option value="Rhode Island">Rhode Island</option>
                        <option value="South Carolina">South Carolina</option>
                        <option value="South Dakota">South Dakota</option>
                        <option value="Tennessee">Tennessee</option>
                        <option value="Texas">Texas</option>
                        <option value="Utah">Utah</option>
                        <option value="Vermont">Vermont</option>
                        <option value="Virginia">Virginia</option>
                        <option value="Washington">Washington</option>
                        <option value="West Virginia">West Virginia</option>
                        <option value="Wisconsin">Wisconsin</option>
                        <option value="Wyoming">Wyoming</option>
                    </select>'
    );

    return $filters;
}

add_filter( 'tribe_events_pre_get_posts', 'setup_my_bar_field_in_query' );

function setup_my_bar_field_in_query( $query ){

    $statevar = $_REQUEST['event_state'];

    if ( !empty( $statevar ) ) {


                  $query->set( 'tax_query', array(

                    array(

                      'taxonomy' => 'post_tag',

                      'field' => 'slug',

                      'terms' => array($statevar),

                      'operator' => 'IN'

                    )

                    )

                  );


    }
    return $query;
}