So what exactly makes a senior lien senior (1st) and a junior (2nd) junior? When referring to a deed of trust, is it the time/date when one was recorded or the dollar amount ?
For example if I take a loan (considering there are no other liens attached) for the amount of $50k on 2/14/18... then later take another loan for $100k on 7/17/18, which is Senior?
The first one I took because it was recorded first or the second at a higher value yet a later date?
The recording date.
Not exactly the recording date in every instance. In certain circumstances a senior lien can be subordinated. The government can place a tax lien on the property and force a sale where the lending institution would have to defend the lien. This can happen with a contractor's lien, though in some instances, those are subordinated.
Finally, a senior lien can become subordinated if they do so by contract. I've seen senior mortgages subordinated when another institution became involved. In those cases it is usually a large build. A case in point was a bank that had a lien on farmland. Their loan was subordinated when the land was developed into a mall. In return for the subordination, the bank may have gotten a higher yield or protection in some manner from loss.