When I took Herpetology in college, we all had to buy a Peterson's Guide for lab. That's where I started. Next, I check this sub multiple times a day and try to ID the snakes.
Do you live near farmland where there is a lot of pesticide use?
This book about frog deformities was really sad to read some years back: https://www.amazon.com/Plague-Frogs-Horrifying-True-Story/dp/0756757541
I got my first beardie earlier this year, breeder recommended this book and so far it’s been very helpful to reference: The Bearded Dragon Manual, 2nd... https://www.amazon.com/dp/1620082535?ref=ppx_pop_mob_ap_share
Also, I highly recommend this book. It is the best book out there and has everything. You can read it whole and use it as a reference manual.
Get yourself this book! It is the bible and works as a reference manual so you dont have to read the whole thing, you can lookup what you need although I suggest reading it
A Field Guide to the Amphibians and Reptiles of the Maya World: The Lowlands of Mexico, Northern Guatemala, and Belize https://www.amazon.com/dp/0801485878/ref=cm_sw_r_awdo_navT_a_F0WFYDTK4NJM9K52MTS1
There are some good field guides that cover your area, and these are better and more efficient to help you learn your local species. You should pick up this one; you can find one used in good condition on eBay or Amazon for $12-
Peterson Field Guide to Reptiles and Amphibians of Eastern and Central North America, 4th Edition
You could also try the older, 3rd Edition Expanded, which is going for $9 used on Amazon. It's behind the times in terms of taxonomy, but it has more pictures, and it also includes more information about many species lifestyles and habits, which might be useful to a young student of the game such as yourself.
The best place to go is your local library. One book I recommend is Salamanders of the United States and Canada. it has accounts of all the known species and lots of good photos.
https://www.amazon.com/Salamanders-United-States-Canada-Petranka/dp/1588343081
Snake head shape is also a bad idea. Most snakes will flatten their head when threatened or preparing to strike. Think of what cobras can do, but not so extreme. This is to puff up and look more threatening. This isn't 100% universal, but a common behavior.
Yes your rattle snakes of the family Crotalidae/Viperidae do have very prominent head shape, but the rattling is such a better way to pick them out. Contrasting, the coral snake, Micrurus tener, has a very round head, looks very similar to milk snakes, however their neurotoxin venom will kill you.
EDIT: Best advice I have is to just pick a field guide of your region and read it. (https://www.amazon.com/Peterson-Reptiles-Amphibians-Eastern-Central/dp/0544129970) Other then that, just let the sneks be sneks and slither away!
I'll just copy and paste what I responded to earlier in the comment thread. Too lazy to type.
"Snake head shape is also a bad idea. Most snakes will flatten their head when threatened or preparing to strike. Think of what cobras can do, but not so extreme. This is to puff up and look more threatening. This isn't 100% universal, but a common behavior.
Yes your rattle snakes of the family Crotalidae/Viperidae do have very prominent head shape, but the rattling is such a better way to pick them out. Contrasting, the coral snake, Micrurus tener, has a very round head, looks very similar to milk snakes, however their neurotoxin venom will kill you.
EDIT: Best advice I have is to just pick a field guide of your region and read it. (https://www.amazon.com/Peterson-Reptiles-Amphibians-Eastern-Central/dp/0544129970) Other then that, just let the sneks be sneks and slither away!"
I would suggest joining COPARC (Colorado Partners in Amphibian and Reptile Conservation) on FB. COPARC has events where a bunch of herpers all get together and go out to find some reptiles and amphibians. Another thing I would suggest is checking out Smetlogik on youtube, he does videos on field herping many of which are based out of Colorado(not many on specific locals or anything though) . If you do decide to join COPARC you could post and ask for some help herping Colorado and I'm sure there would be some people happy to help!
On a last side note I would suggest getting a Colorado field guide for reptiles and amphibians. I personally think that Amphibians and Reptiles in Colorado, Revised Edition Paperback – November 1, 1999 by Geoffrey A. Hammerson is the best version. http://www.amazon.com/Amphibians-Reptiles-Colorado-Revised-Edition/dp/0870815342
As far as my personally advice, in the city garters can be found around ponds or streams on warm days basking, as for the rest you have to leave Denver proper to really get to much.