I understand you can filter the results based on country or city, but is anyone aware of how to do this to filter by USA state? Or a workaround of some kind?

This is how I currently limit by country.

$query['dimensionFilterClauses'] = ['filters' => [
        [
            "dimension_name" => "ga:country",
            "operator" => 'PARTIAL',
            "expressions" => 'United States'
        ]
    ]
];

$body = new \Google_Service_AnalyticsReporting_GetReportsRequest();
$body->setReportRequests( array($query) );

$client = new \Google_Client();
$client->setApplicationName("Analytics Reporting");
$analytics = new \Google_Service_AnalyticsReporting($client);

$response = $analytics->reports->batchGet( $body );