Here is a caterpillar found on our sidewalk in Longmont, Colorado. Right click for full resolution. This particular caterpillar appears to be the larva of the variegated fritillary (Euptoieta claudia) butterfly, which is found from British Columbia to Argentina. Its dimensions were approximately 6 mm wide (including appendages) by 30 mm long.
Equipment used: Canon EOS Rebel T5i with a standard zoom lens (EF-S 18-55 mm).