Colorado 300 comes with a built-in worldwide basemap with
shaded relief and accepts SD cards for all your outdoor
activities on land or water. Just take your pick from
Garmin’s preprogrammed SD cards including street maps,
topographic maps, coastal charts or inland lake data. The
card slot is located inside the waterproof battery
compartment, so you don't have to worry about getting it
wet.
Colorado 300 has a built-in electronic compass that provides
bearing information even while you're standing still, and its barometric
altimeter tracks changes in pressure to pinpoint your precise altitude.
Intuitive and fun, Colorado features a Rock ‘n Roller® input
wheel for easy one-handed operation and supports
Geocaching.com GPX
files for downloading geocaches and detail straight to your unit.
Purchase:
Costo had the Colorado 300 on special for $249 after a $50
instant rebate. Not bad for a GPS that has a $499.99 MSRP.
Topo Maps:
I decided to bite the bullet and get the California and
Nevada Topographic map on SD card (TOPO US 24K West
Micro SD Card). I found it on eBay for $75 including shipping.
Geocaching:
I was able to download Geocache coordinates directly and
easily to the Garmin Colorado 300 from the Geocaching.com website. I
decided to upgrade my Geocaching membership to premium for $30/year.
This allows not only the name and coordinates, but the description and hint
to be downloaded as well. If you are into Geocaching, this is worth its
weight in gold.
Mountain Biking:

I purchased a Garmin Colorado Handlebar Mount at REI for
$9.95. Nothing flashy, but it works decently well and allows the GPS
to be removed pretty easily.
The Colorado 300 has a nice sized screen so it was easy to
read while riding.
Off-roading: