Unable to call specific dynamic_sidebar

First, let’s make sure we’re clear regarding terminology; there are two possible meanings for “sidebar” in your question:

1. A dynamic sidebar, i.e. a Widget area, created via call to register_sidebar() in functions.php, and included in the template via call to dynamic_sidebar().
2. A template part, called via get_sidebar( $slug ), the markup of which is defined in a template-part file named sidebar-$slug.php.

The two can, but do not have to, be related. For instance, calls to dynamic_sidebar() can, but do not have, to reside within a sidebar-$slug.php template-part file.

Let’s step through both scenarios:

Dynamic Sidebar “Mountain”

So, assuming that your “Mountain” sidebar is a Widget area, you’ll have something like the following defined in functions.php:

<?php
function wpse46048_register_dynamic_sidebars() {
    // Register "Mountain" Widget area
    register_sidebar( array( 
        'name' => 'Mountain',
        'id' => 'mountain',
        'description' => 'Mountain Widget area',
        'before_widget' => '<div id="%1$s" class="widget %2$s">',
        'after_widget' => '</div>',
        'before_title' => '<div class="title widgettitle">',
        'after_title' => '</div>',
    ) );
}
add_action( 'widgets_init', 'wpse46048_register_dynamic_sidebars' );
?>

…and then, somewhere in your template, you will call either this:

<?php
if ( ! dynamic_sidebar( 'mountain' ) ) :
    // Default content output goes here
endif;
?>

…or else just this (if you don’t want to output any default content):

<?php dynamic_sidebar( 'mountain' ); ?>

Then, you would populate the Widgets for this area via Dashboard -> Appearance -> Widgets, by dragging-and-dropping Widgets into the “Mountain” Widget area.

Template-part Sidebar “Mountain”

Assuming that your “Mountain” sidebar is a template part, you’ll first define the markup for that template part in a file called sidebar-mountain.php. Then, you’ll include that template-part file in the template via:

<?php get_sidebar( 'mountain' ); ?>