Well, it depends on what you mean by "valid".
Are you afforded the same protection in the US as you are in Spain? No.
However, you can apply for protection in the US under what is know as the Madrid protocol. It is called the Madrid Protocol only because that's where all the member nations (80-90 of them) convened for the conference that resulted in the treaty, not because of your Spanish mark.
Under the "Madrid in", as it's known in the trade, you would apply for your US TM via WIPO as an international application. Then, you are able to apply the "priority" rule and your mark is given a cleaner way through the process.
Otherwise, just start fresh with a USPTO application, without using the Spanish mark.
But, hey, even though I've done 35 TM applications on my own, I do have a lawyer in the US for a mark I am bringing into the US on the "Madrid in" international application. It's worth it.
Hope this helps.
Steve