Set a default full-width layout in a Genesis child theme

full-width-default-layout.php

<?php

add_filter( 'genesis_theme_settings_defaults', 'prefix_default_full_width_layout' );
/**
 * Set a full-width layout as the default in a Genesis Child theme.
 *
 * @author   Robert Neu
 * @see      Genesis_Admin_Settings in genesis/lib/admin/theme-settings.php
 */
function prefix_default_full_width_layout( $settings ) {
	$settings['site_layout'] = 'full-width-content';
	return $settings;
}