<?php
$tz = new DateTimeZone('America/Denver');
$now = new DateTime('August 31', $tz);
echo 'today ' . $now->format('M-d');
$now->modify('first day this month');
echo 'first ' .$now->format('M-d');
$now->modify('last day this month');
$now->modify('first day this month');
echo 'first after last ' .$now->format('M-d');